We utilize operando X-ray computed tomography, coupled with real-time electrochemical analysis, to reveal the underlying failure mechanisms of membrane electrode assemblies (MEAs) for electrochemical CO2 reduction (eCO2R). Through operando imaging, we can obtain unprecedented insights into the dynamic behavior of the MEA under different operating conditions, revealing critical changes in interface interactions, phase distribution, and structural integrity over time. Our findings identify phenomena giving rise to the transition from CO2R to the hydrogen evolution reaction (HER), as evidenced by shifts in cathode potential and CO2R selectivity. The formation of inhomogeneous precipitates at the gas diffusion electrode disrupts the CO2 supply and reduces the active sites for eCO2R, resulting in a shift toward H2 production during low current density operation. Additionally, under high current density conditions, rapid water crossover up to the microporous layer/gas diffusion layer promotes the transition from CO2R to HER, further shifting cell potential toward anodic direction. Oscillating voltage conditions reveal the dissolution and regrowth of precipitates, providing direct visualization of the competing selectivity of CO2R and HER. This work offers new insight into the degradation mechanisms of MEAs, with implications for the design of more durable CO2R systems.
", "doi": "10.1039/d5ey00232j", "issn": "2753-801X", "publisher": "Royal Society of Chemistry", "publication": "EES Catalysis", "publication_date": "2025" }, { "id": "authors:afx9x-mza95", "collection": "authors", "collection_id": "afx9x-mza95", "cite_using_url": "https://authors.library.caltech.edu/records/afx9x-mza95", "type": "article", "title": "Asymmetric Bipolar Membrane for High Current Density Electrodialysis Operation with Exceptional Stability", "author": [ { "family_name": "Lucas", "given_name": "\u00c9owyn", "orcid": "0000-0002-8743-5722", "clpid": "Lucas-\u00c9owyn" }, { "family_name": "Bui", "given_name": "Justin C.", "orcid": "0000-0003-4525-957X" }, { "family_name": "Stovall", "given_name": "Timothy Nathan" }, { "family_name": "Hwang", "given_name": "Monica", "clpid": "Hwang-Monica" }, { "family_name": "Wang", "given_name": "Kaiwen", "clpid": "Wang-Kaiwen" }, { "family_name": "Dunn", "given_name": "Emily R.", "clpid": "Dunn-Emily-R" }, { "family_name": "Spickermann", "given_name": "Ellis", "clpid": "Spickermann-Ellis-A" }, { "family_name": "Shiau", "given_name": "Lily", "clpid": "Shiau-Lily" }, { "family_name": "Kusoglu", "given_name": "Ahmet", "orcid": "0000-0002-2761-1050" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624" }, { "family_name": "Bell", "given_name": "Alexis T.", "orcid": "0000-0002-5738-4645" }, { "family_name": "Ardo", "given_name": "Shane", "orcid": "0000-0001-7162-6826" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Bipolar membranes (BPMs) enable isolated acidic/alkaline regions in electrochemical devices, facilitating optimized environments for electrochemical separations and catalysis. For economic viability, BPMs must attain stable, high current density operation with low overpotentials in a freestanding configuration. We report an asymmetric, graphene oxide (GrOx)-catalyzed BPM capable of freestanding electrodialysis operation at 1 A cm–2 with overpotentials <250 mV. Use of a thin anion-exchange layer improves water transport while maintaining near unity Faradaic efficiency for acid and base generation. Voltage stability exceeding 1100 h with an average drift of 70 μV/h at 80 mA cm–2 and 100 h with an average drift of −300 μV/h at 500 mA cm–2 and implementation in an electrodialysis stack demonstrate real-world applicability. Continuum modeling reveals that water dissociation in GrOx BPMs is both catalyzed and electric-field enhanced, where low pKa moieties on GrOx enhance local electric fields and high pKa moieties serve as active sites for surface-catalyzed water dissociation. These results establish commercially viable BPM electrodialysis and provide fundamental insight to advance design of next-generation devices.
", "doi": "10.1021/acsenergylett.4c01662", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2024-11-08", "series_number": "11", "volume": "9", "issue": "11", "pages": "5596-5605" }, { "id": "authors:c6455-b6n11", "collection": "authors", "collection_id": "c6455-b6n11", "cite_using_url": "https://authors.library.caltech.edu/records/c6455-b6n11", "type": "article", "title": "Analysis of bipolar membranes for electrochemical CO\u2082 capture from air and oceanwater", "author": [ { "family_name": "Bui", "given_name": "Justin C.", "orcid": "0000-0003-4525-957X", "clpid": "Bui-Justin-C" }, { "family_name": "Lucas", "given_name": "\u00c9owyn", "orcid": "0000-0002-8743-5722", "clpid": "Lucas-\u00c9owyn" }, { "family_name": "Lees", "given_name": "Eric W.", "orcid": "0000-0002-0524-3816", "clpid": "Lees-Eric-W" }, { "family_name": "Liu", "given_name": "Andrew K.", "orcid": "0000-0001-6598-7254", "clpid": "Liu-Andrew-K" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Bell", "given_name": "Alexis T.", "orcid": "0000-0002-5738-4645", "clpid": "Bell-Alexis-T" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-Adam-Z" } ], "abstract": "Carbon dioxide (CO\u2082) must be removed from the atmosphere to mitigate the negative effects of climate change. However, the most scalable methods for removing CO\u2082 from the air require heat from fossil-fuel combustion to produce pure CO\u2082 and continuously regenerate the sorbent. Bipolar-membrane electrodialysis (BPM-ED) is a promising technology that uses renewable electricity to dissociate water into acid and base to regenerate bicarbonate-based CO\u2082 capture solutions, such as those used in chemical loops of direct-air-capture (DAC) processes, and in direct-ocean capture (DOC) to promote atmospheric CO\u2082 drawdown via decarbonization of the shallow ocean. In this study, we develop an experimentally validated 1D model for the electrochemical regeneration of CO\u2082 from bicarbonate-based carbon capture solutions and seawater using BPM-ED. For DAC, our experimental and computational results demonstrate that pH swings induced by BPM water dissociation drive the formation of CO\u2082 at the cation-exchange layer|catholyte interface with energy-intensities of less than 150 kJ mol\u207b\u00b9. However, high rates of bubble formation increase energy intensity at current densities >100 mA cm\u207b\u00b2. Correspondingly, accelerating water dissociation catalysis and enacting bubble removal could enable CO\u2082 recovery at energy intensities <100 kJ mol\u207b\u00b9 and current densities >100 mA cm\u207b\u00b2. For DOC, mass transport limitations associated with low carbon concentrations in oceanwater suggest that DOC is best suited for clean production of acid and base usable in downstream processes. These results provide design principles for industrial-scale CO\u2082 recovery using BPM-ED.
", "doi": "10.1039/d3ee01606d", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy & Environmental Science", "publication_date": "2023-11", "series_number": "11", "volume": "16", "issue": "11", "pages": "5076-5095" }, { "id": "authors:2v96x-s0579", "collection": "authors", "collection_id": "2v96x-s0579", "cite_using_url": "https://authors.library.caltech.edu/records/2v96x-s0579", "type": "article", "title": "Tuning the Interfacial Electrical Field of Bipolar Membranes with Temperature and Electrolyte Concentration for Enhanced Water Dissociation", "author": [ { "family_name": "Zhang", "given_name": "Huanlei", "clpid": "Zhang-Huanlei" }, { "family_name": "Cheng", "given_name": "Dongbo", "clpid": "Cheng-Dongbo" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lin", "given_name": "Meng", "orcid": "0000-0001-7785-749X", "clpid": "Lin-Meng" } ], "abstract": "A coupled experimental and numerical study was performed for a fundamental understanding of the impact of operating conditions, i.e., temperature and electrolyte concentration, as well as interfacial abruptness, on the bipolar membrane (BPM) performance. A comprehensive multiphysics-based model was developed to optimize the operation condition and interfacial properties of BPM, and the model was used to guide the design and engineering of high-performing BPMs. The origin of the enhanced BPM performance at a high temperature was identified, which was attributed to the intrinsic reaction rate enhancement as well as the increase in electrolyte ionic conductivity. The experimentally demonstrated current density–voltage characteristics of BPMs clearly exhibited three distinctive regions of operation: ion-crossover region, water dissociation region, and water-limiting region, which agreed well with the multiphysics simulation results. In addition, the model revealed that a sharper interfacial abruptness led to improved BPM performance due to the enhanced interfacial electric field at the water dissociation region. The decrease of the electrolyte concentration, which increased the dielectric constant of the electrolyte, enhanced the interfacial electric field, leading to improved electrochemical performances. The present study offers an in-depth perspective to understand the species transport as well as water dissociation mechanism under various operation conditions and membrane designs, providing the optimal operation conditions and membrane designs for maximizing the BPM performance at high current densities.
", "doi": "10.1021/acssuschemeng.3c00142", "issn": "2168-0485", "publisher": "American Chemical Society", "publication": "ACS Sustainable Chemistry & Engineering", "publication_date": "2023-05-29", "series_number": "21", "volume": "11", "issue": "21", "pages": "8044-8054" }, { "id": "authors:aa3jd-fbh80", "collection": "authors", "collection_id": "aa3jd-fbh80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230411-764712100.15", "type": "article", "title": "Editorial: Advanced water splitting technologies development: Best practices and protocols", "author": [ { "family_name": "Bulfin", "given_name": "Brendan", "orcid": "0000-0001-9361-0075", "clpid": "Bulfin-Brendan" }, { "family_name": "Carmo", "given_name": "Marcelo", "orcid": "0000-0002-0186-317X", "clpid": "Carmo-Marcelo" }, { "family_name": "Van de Krol", "given_name": "Roel", "orcid": "0000-0003-4399-399X", "clpid": "van-de-Krol-Roel" }, { "family_name": "Mougin", "given_name": "Julie", "orcid": "0000-0002-3594-3506", "clpid": "Mougin-Julie" }, { "family_name": "Ayers", "given_name": "Kathy", "clpid": "Ayers-Kathy" }, { "family_name": "Gross", "given_name": "Karl J.", "clpid": "Gross-Karl-J" }, { "family_name": "Marina", "given_name": "Olga A.", "orcid": "0000-0002-8176-7099", "clpid": "Marina-Olga-A" }, { "family_name": "Roberts", "given_name": "George M.", "clpid": "Roberts-George-M" }, { "family_name": "Stechel", "given_name": "Ellen B.", "orcid": "0000-0002-5379-2908", "clpid": "Stechel-Ellen-B" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "As the level of deployment and utilization of renewable energy sources, including wind and solar, continues to rise, large-scale, long-term energy storage technologies that could accommodate weekly and seasonal energy fluctuations will play a significant role in the overall deployment of renewable energies in the future. Harnessing and storing renewable energy resources via electrochemical, photoelectrochemical, or thermochemical processes by converting renewable energy into sustainable (energy storage) fuels have the potential to meet the long-term, terawatt scale energy storage challenge. Renewable hydrogen production is the cornerstone for sustainable fuel production and deep decarbonization of multiple sectors in our society. Cost-competitive clean hydrogen provides value to applications, such as 1) in the transportation sector for fuel cell vehicles, 2) in the electric grid sector for system stability and load balancing, and 3) in the industrial sector with metal refineries, cement production, and biomass upgrading (carbon-free fertilizer production). In addition, coupling clean renewable hydrogen with the carbon and nitrogen cycles enables known and well-established thermal-chemical processes to generate renewable hydrocarbon fuels and ammonia. The Advanced Water Splitting Technologies (AWST): low temperature electrolysis (LTE), high temperature electrolysis (HTE), photoelectrochemical (PEC) and solar thermo-chemical hydrogen (STCH) provide four unique and parallel approaches to produce low cost, low greenhouse gas (GHG) emission hydrogen at scale (Figure 1). Cost competitive clean hydrogen production using these four technologies is a current high priority focus for governments and industry. In June of 2022, the U.S. Department of Energy (DOE) launched the first in a series of Earthshot Initiatives. The Hydrogen Shot, \"1 1 1\" aims to reduce the cost of clean hydrogen by more than 80% to one dollar per one kilogram in 1 decade ($1/kg H\u2082). The European Green Deal and the International Energy Agency (IEA) have implemented a strong focus on green hydrogen production for a clean and secure energy future.", "doi": "10.3389/fenrg.2023.1149688", "issn": "2296-598X", "publisher": "Frontiers Media", "publication": "Frontiers in Energy Research", "publication_date": "2023-03-06", "volume": "11", "pages": "Art. No. 1149688" }, { "id": "authors:4m1sh-azw58", "collection": "authors", "collection_id": "4m1sh-azw58", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221031-575730600.41", "type": "article", "title": "Comparative Study on Electrochemical and Thermochemical Pathways for Carbonaceous Fuel Generation Using Sunlight and Air", "author": [ { "family_name": "Xu", "given_name": "Da", "clpid": "Xu-Da" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lin", "given_name": "Meng", "orcid": "0000-0001-7785-749X", "clpid": "Lin-Meng" } ], "abstract": "A comparative study on the solar-to-fuel (STF) conversion efficiency of electrochemical and thermochemical approaches for methane (CH\u2084), methanol (MeOH), and ethanol (EtOH) generation using sunlight and air was performed. The system level STF conversion efficiency studied herein took into account of both the conversion processes and feedstock capture processes. In particular, the feedstock, CO\u2082 and H\u2082O, in this analysis were assumed to be captured from air. For thermochemical conversion, one and two-step approaches were considered including CH\u2084 generation from the Sabatier reaction, and two-step processes for methanol (MeOH) and ethanol (EtOH) generation from CO and H\u2082 coupled with the reverse water gas shift reaction (rWGS). State-of-the-art electrochemical and hybrid electrochemical-thermochemical processes for CH\u2084, MeOH and EtOH generation, and the corresponding system level STF conversion efficiency were then compared and contrasted to the thermochemical approaches. Target overpotentials and Faradaic efficiency (FE) for the electrochemical CO\u2082 reduction reactions was also presented to compete with thermochemical approaches at different operating scenarios.", "doi": "10.1021/acssuschemeng.2c03230", "issn": "2168-0485", "publisher": "American Chemical Society", "publication": "ACS Sustainable Chemistry & Engineering", "publication_date": "2022-10-24", "series_number": "42", "volume": "10", "issue": "42", "pages": "13945-13954" }, { "id": "authors:35y2d-s2y96", "collection": "authors", "collection_id": "35y2d-s2y96", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221208-575982500.9", "type": "article", "title": "Challenges and opportunities in continuous flow processes for electrochemically mediated carbon capture", "author": [ { "family_name": "Liu", "given_name": "Yayuan", "clpid": "Liu-Yayuan" }, { "family_name": "Lucas", "given_name": "\u00c9owyn", "orcid": "0000-0002-8743-5722", "clpid": "Lucas-\u00c9owyn" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Li", "given_name": "Xing", "clpid": "Li-Xing" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Carbon capture from both stationary emitters and dilute sources is critically needed to mitigate climate change. Carbon dioxide separation methods driven by electrochemical stimuli show promise to sidestep the high-energy penalty and fossil-fuel dependency associated with the conventional pressure and temperature swings. Compared with a batch process, electrochemically mediated carbon capture (EMCC) operating in a continuous flow mode offers greater design flexibility. Therefore, this review introduces key advances in continuous flow EMCC for point source, air, and ocean carbon captures. Notably, the main challenges and future research opportunities for practical implementation of continuous flow EMCC processes are discussed from a multi-scale perspective, from molecules to electrochemical cells and finally to separation systems.", "doi": "10.1016/j.isci.2022.105153", "pmcid": "PMC9529983", "issn": "2589-0042", "publisher": "Elsevier", "publication": "iScience", "publication_date": "2022-10-21", "series_number": "10", "volume": "25", "issue": "10", "pages": "Art. No. 105153" }, { "id": "authors:dbr6r-15w44", "collection": "authors", "collection_id": "dbr6r-15w44", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221212-795726500.2", "type": "article", "title": "Measurement of ion transport properties in ion exchange membranes for photoelectrochemical water splitting", "author": [ { "family_name": "Lucas", "given_name": "\u00c9owyn", "orcid": "0000-0002-8743-5722", "clpid": "Lucas-\u00c9owyn" }, { "family_name": "Han", "given_name": "Lihao", "orcid": "0000-0002-0452-3381", "clpid": "Han-Lihao" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Photoelectrochemical (PEC) water-splitting systems have the unique ability to produce renewable hydrogen directly from sunlight, independent of the electrical grid. These systems are therefore appealing technological options for resilient long-term energy storage. Ion selective membranes, such as monopolar and bipolar membranes, are a vital component of PEC water-splitting systems. These membranes allow for ionic conduction between the cathode and anode chambers, separation of products, and improved catalyst environments for reactions. In order to measure key properties and to study the performance of these ion exchange membranes, it is imperative to develop a robust testing protocol that can be used across the field. This paper introduces two standard electrochemical cells designed to directly measure ion transport properties in monopolar and bipolar membranes. The first electrochemical cell uses commercially available Pt disk electrodes to preform electrochemical impedance spectroscopy (EIS) and reliably measure through-plane conductivity of monopolar membranes. The second electrochemical cell uses four-point measurements with Luggin capillaries and a series of membrane configurations to perform current density-voltage and Faradaic efficiency (FE) measurements for water dissociation (WD) reactions on bipolar membranes. The cell designs and techniques laid out below allow for accurate measurement of ion transport parameters in ion exchange membranes, direct comparison of membranes being developed across the field, and in turn, greater advancements in ion exchange membranes and PEC water-splitting systems.", "doi": "10.3389/fenrg.2022.1001684", "issn": "2296-598X", "publisher": "Frontiers Media", "publication": "Frontiers in Energy Research", "publication_date": "2022-09-14", "volume": "10", "pages": "Art. No. 1001684" }, { "id": "authors:83tv1-p3k51", "collection": "authors", "collection_id": "83tv1-p3k51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220608-849360000", "type": "article", "title": "The 2022 solar fuels roadmap", "author": [ { "family_name": "Segev", "given_name": "Gideon", "orcid": "0000-0002-6175-3458", "clpid": "Segev-Gideon" }, { "family_name": "Kibsgaard", "given_name": "Jakob", "orcid": "0000-0002-9219-816X" }, { "family_name": "Hahn", "given_name": "Christopher", "orcid": "0000-0002-2772-6341" }, { "family_name": "Xu", "given_name": "Zhichuan J.", "orcid": "0000-0001-7746-5920" }, { "family_name": "Cheng", "given_name": "Wen-Hui", "orcid": "0000-0003-3233-4606" }, { "family_name": "Deutsch", "given_name": "Todd G.", "orcid": "0000-0001-6577-1226" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Zhang", "given_name": "Jenny Z.", "orcid": "0000-0003-4407-5621" }, { "family_name": "Hammarstrom", "given_name": "Leif", "orcid": "0000-0002-9933-9084" }, { "family_name": "Nocera", "given_name": "Daniel G.", "orcid": "0000-0001-5055-320X" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624" }, { "family_name": "Agbo", "given_name": "Peter", "orcid": "0000-0003-3066-4791" }, { "family_name": "Hisatomi", "given_name": "Takashi", "orcid": "0000-0002-5009-2383" }, { "family_name": "Osterloh", "given_name": "Frank E.", "orcid": "0000-0002-9288-3407" }, { "family_name": "Domen", "given_name": "Kazunari", "orcid": "0000-0001-7995-4832" }, { "family_name": "Abdi", "given_name": "Fatwa F.", "orcid": "0000-0001-5631-0620" }, { "family_name": "Haussener", "given_name": "Sophia", "orcid": "0000-0002-3044-1662" }, { "family_name": "Miller", "given_name": "Daniel J." }, { "family_name": "Ardo", "given_name": "Shane", "orcid": "0000-0001-7162-6826" }, { "family_name": "McIntyre", "given_name": "Paul C.", "orcid": "0000-0002-7498-831X" }, { "family_name": "Hannappel", "given_name": "Thomas", "orcid": "0000-0002-6307-9831" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169" }, { "family_name": "Atwater", "given_name": "Harry", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" }, { "family_name": "Ertem", "given_name": "Mehmed Z.", "orcid": "0000-0003-1994-9024" }, { "family_name": "Sharp", "given_name": "Ian D.", "orcid": "0000-0001-5238-7487" }, { "family_name": "Choi", "given_name": "Kyoung-Shin", "orcid": "0000-0003-1945-8794" }, { "family_name": "Lee", "given_name": "Jae Sung" }, { "family_name": "Ishitani", "given_name": "Osamu", "orcid": "0000-0001-9557-7854" }, { "family_name": "Ager", "given_name": "Joel W.", "orcid": "0000-0001-9334-9751" }, { "family_name": "Prabhakar", "given_name": "Rajiv Ramanujam", "orcid": "0000-0002-4598-9073" }, { "family_name": "Bell", "given_name": "Alexis T.", "orcid": "0000-0002-5738-4645" }, { "family_name": "Boettcher", "given_name": "Shannon W.", "orcid": "0000-0001-8971-9123" }, { "family_name": "Vincent", "given_name": "Kylie", "orcid": "0000-0001-6444-9382" }, { "family_name": "Takanabe", "given_name": "Kazuhiro", "orcid": "0000-0001-5374-9451" }, { "family_name": "Artero", "given_name": "Vincent", "orcid": "0000-0002-6148-8471" }, { "family_name": "Napier", "given_name": "Ryan", "orcid": "0000-0003-1602-7825" }, { "family_name": "Roldan Cuenya", "given_name": "Beatriz", "orcid": "0000-0002-8025-307X" }, { "family_name": "Koper", "given_name": "Marc T. M.", "orcid": "0000-0001-6777-4594" }, { "family_name": "van de Krol", "given_name": "Roel", "orcid": "0000-0003-4399-399X" }, { "family_name": "Houle", "given_name": "Frances", "orcid": "0000-0001-5571-2548" } ], "abstract": "Renewable fuel generation is essential for a low carbon footprint economy. Thus, over the last five decades, a significant effort has been dedicated towards increasing the performance of solar fuels generating devices. Specifically, the solar to hydrogen efficiency of photoelectrochemical cells has progressed steadily towards its fundamental limit, and the faradaic efficiency towards valuable products in CO\u2082 reduction systems has increased dramatically. However, there are still numerous scientific and engineering challenges that must be overcame in order to turn solar fuels into a viable technology. At the electrode and device level, the conversion efficiency, stability and products selectivity must be increased significantly. Meanwhile, these performance metrics must be maintained when scaling up devices and systems while maintaining an acceptable cost and carbon footprint. This roadmap surveys different aspects of this endeavor: system benchmarking, device scaling, various approaches for photoelectrodes design, materials discovery, and catalysis. Each of the sections in the roadmap focuses on a single topic, discussing the state of the art, the key challenges and advancements required to meet them. The roadmap can be used as a guide for researchers and funding agencies highlighting the most pressing needs of the field.", "doi": "10.1088/1361-6463/ac6f97", "issn": "0022-3727", "publisher": "IOP", "publication": "Journal of Physics D: Applied Physics", "publication_date": "2022-08-11", "series_number": "32", "volume": "55", "issue": "32", "pages": "Art. No. 323003" }, { "id": "authors:0t6c2-g9010", "collection": "authors", "collection_id": "0t6c2-g9010", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220202-544247000", "type": "article", "title": "Probing the Catalytically Active Region in a Nanoporous Gold Gas Diffusion Electrode for Highly Selective Carbon Dioxide Reduction", "author": [ { "family_name": "Fenwick", "given_name": "Aidan Q.", "orcid": "0000-0003-4442-0878", "clpid": "Fenwick-Aidan-Q" }, { "family_name": "Welch", "given_name": "Alex J.", "orcid": "0000-0003-2132-9617", "clpid": "Welch-Alex-J" }, { "family_name": "Li", "given_name": "Xueqian", "orcid": "0000-0002-1197-3743", "clpid": "Li-Xueqian" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "DuChene", "given_name": "Joseph S.", "orcid": "0000-0002-7145-323X", "clpid": "DuChene-Joseph-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "abstract": "We report the use of a nanoporous gold (np-Au) catalyst for CO\u2082 reduction in a gas diffusion electrode (GDE) and characterize the role of wetting in electrochemical performance. The np-Au catalyst has pores on the order of 20 nm and is cross-sectionally isotropic, enabling Faradaic efficiencies for CO of greater than 95% across a wide range of potentials and a maximum partial current density for CO of 168 mA/cm\u00b2. Secondary ion mass spectroscopy and in situ copper underpotential deposition were employed to provide insights into catalyst wetting. At a typical CO\u2082 flow rate of 50 SCCM, approximately half of the catalyst is in contact with the electrolyte during operation, and the dry region exists in the bottom half of the nanoporous catalyst. We discuss implications of the nanoporous GDE wetting characteristics for catalyst performance and the design of improved GDE architectures that can maximize the catalytically active area.", "doi": "10.1021/acsenergylett.1c02267", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2022-02-11", "series_number": "2", "volume": "7", "issue": "2", "pages": "871-879" }, { "id": "authors:sb1ng-8ew27", "collection": "authors", "collection_id": "sb1ng-8ew27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220309-676764000", "type": "article", "title": "Comprehensive Evaluation for Protective Coatings: Optical, Electrical, Photoelectrochemical, and Spectroscopic Characterizations", "author": [ { "family_name": "Shen", "given_name": "Xin", "clpid": "Shen-Xin" }, { "family_name": "Yanagi", "given_name": "Rito", "clpid": "Yanagi-Rito" }, { "family_name": "Solanki", "given_name": "Devan", "clpid": "Solanki-Devan" }, { "family_name": "Su", "given_name": "Haoqing", "clpid": "Su-Haoqing" }, { "family_name": "Li", "given_name": "Zhaohan", "orcid": "0000-0002-8155-7243", "clpid": "Li-Zhaohan" }, { "family_name": "Xiang", "given_name": "Cheng-Xiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" } ], "abstract": "Numerous efficient semiconductors suffer from instability in aqueous electrolytes. Strategies utilizing protective coatings have thus been developed to protect these photoabsorbers against corrosion while synergistically improving charge separation and reaction kinetics. Recently, various photoelectrochemical (PEC) protective coatings have been reported with suitable electronic properties to ensure low charge transport loss and reveal the fundamental photoabsorber efficiency. However, protocols for studying the critical figures of merit for protective coatings have yet to be established. For this reason, we propose four criteria for evaluating the performance of a protective coating for PEC water-splitting: stability, conductivity, optical transparency, and energetic matching. We then propose a flow chart that summarizes the recommended testing protocols for quantifying these four performance metrics. In particular, we lay out the stepwise testing protocols to evaluate the energetics matching at a semiconductor/coating/(catalyst)/liquid interface. Finally, we provide an outlook for the future benchmarking needs for coatings.", "doi": "10.3389/fenrg.2021.799776", "issn": "2296-598X", "publisher": "Frontiers Media SA", "publication": "Frontiers in Energy Research", "publication_date": "2022-01-12", "volume": "9", "pages": "Art. No. 799776" }, { "id": "authors:pwzbv-01469", "collection": "authors", "collection_id": "pwzbv-01469", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211122-153022306", "type": "article", "title": "Coupling electrochemical CO\u2082 conversion with CO\u2082 capture", "author": [ { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Goryachev", "given_name": "Andrey", "orcid": "0000-0001-5280-4850", "clpid": "Goryachev-Andrey" }, { "family_name": "Digdaya", "given_name": "Ibadillah A.", "orcid": "0000-0001-7349-0934", "clpid": "Digdaya-Ibadillah-A" }, { "family_name": "Li", "given_name": "Xueqian", "orcid": "0000-0002-1197-3743", "clpid": "Li-Xueqian" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Vermaas", "given_name": "David A.", "orcid": "0000-0002-4705-6453", "clpid": "Vermaas-David-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Electrochemical CO\u2082 conversion into fuels or chemicals and CO\u2082 capture from point or dilute sources are two important processes to address the gigaton challenges in reducing greenhouse gas emissions. Both CO\u2082 capture and electrochemical CO\u2082 conversion are energy intensive, and synergistic coupling between the two processes can improve the energy efficiency of the system and reduce the cost of the reduced products, via eliminating the CO\u2082 transport and storage or eliminating the capture media regeneration and molecular CO\u2082 release. We consider three different levels to couple electrochemical CO\u2082 reduction with CO\u2082 capture: independent (Type-I), subsequent (Type-II) and fully integrated (Type-III) capture and conversion processes. We focus on Type-II and Type-III configurations and illustrate potential coupling routes of different capture media, which include amine-based solutions and direct carbamate reduction, redox active carriers, aqueous carbonate and bicarbonate solutions, ionic liquids CO\u2082 capture and conversion mediated by covalent organic frameworks.", "doi": "10.1038/s41929-021-00699-7", "issn": "2520-1158", "publisher": "Nature Publishing Group", "publication": "Nature Catalysis", "publication_date": "2021-11", "series_number": "11", "volume": "4", "issue": "11", "pages": "952-958" }, { "id": "authors:95hh3-zeb55", "collection": "authors", "collection_id": "95hh3-zeb55", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210917-215610705", "type": "article", "title": "Operando Local pH Measurement within Gas Diffusion Electrodes Performing Electrochemical Carbon Dioxide Reduction", "author": [ { "family_name": "Welch", "given_name": "Alex J.", "orcid": "0000-0003-2132-9617", "clpid": "Welch-Alex-J" }, { "family_name": "Fenwick", "given_name": "Aidan Q.", "orcid": "0000-0003-4442-0878", "clpid": "Fenwick-Aidan-Q" }, { "family_name": "B\u00f6hme", "given_name": "Annette", "orcid": "0000-0003-1109-3428", "clpid": "B\u00f6hme-Annette" }, { "family_name": "Chen", "given_name": "Hsiang-Yun", "orcid": "0000-0002-6461-1519", "clpid": "Chen-Hsiang-Yun" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Li", "given_name": "Xueqian", "orcid": "0000-0002-1197-3743", "clpid": "Li-Xueqian" }, { "family_name": "DuChene", "given_name": "Joseph S.", "orcid": "0000-0002-7145-323X", "clpid": "DuChene-Joseph-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "abstract": "The local pH near the surface of a CO\u2082 reduction electrocatalyst strongly impacts catalytic selectivity and activity. Here, confocal fluorescence microscopy was used to map the electrolyte pH near a copper gas diffusion electrode during CO\u2082 reduction with micron spatial resolution in three dimensions. We observed that the local pH increased from pH 6.8 to greater than pH 10 as the current density was increased from 0 to 28 mA/cm\u00b2 in a 100 mM KHCO\u2083 electrolyte. Variations in the pH across the surface indicate areas of locally increased activity. Within deep trenches of the active layer, the local pH increases as trench width decreases. Computational models confirm these experimental results and also showed that the catalyst found within narrow trenches is more active than that found at the surface of the electrode. This study suggests that the overpotential required to perform selective CO\u2082 reduction can be reduced by increasing the density of narrow trench regions in the microporous layer.", "doi": "10.1021/acs.jpcc.1c06265", "issn": "1932-7447", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry C", "publication_date": "2021-09-30", "series_number": "38", "volume": "125", "issue": "38", "pages": "20896-20904" }, { "id": "authors:ggeb0-5jc40", "collection": "authors", "collection_id": "ggeb0-5jc40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210830-230028535", "type": "article", "title": "Hydrogen from Sunlight and Water: A Side-by-Side Comparison between Photoelectrochemical and Solar Thermochemical Water-Splitting", "author": [ { "family_name": "Cheng", "given_name": "Wen-Hui", "orcid": "0000-0003-3233-4606", "clpid": "Cheng-Wen-Hui" }, { "family_name": "de la Calle", "given_name": "Alberto", "orcid": "0000-0002-5510-7943", "clpid": "de-la-Calle-Alberto" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Stechel", "given_name": "Ellen B.", "orcid": "0000-0002-5379-2908", "clpid": "Stechel-Ellen-B" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Photoelectrochemical (PEC) and solar thermochemical (STCH) water-splitting represent two promising pathways for direct solar hydrogen generation. PEC water-splitting integrates multiple functional materials and utilizes energetic electrons and holes generated from sunlight to produce hydrogen and oxygen in two half-reactions, while STCH water-splitting couples a series of consecutive chemical reactions and uses absorbed heat from sunlight to generate hydrogen and oxygen in two full reactions. In this Focus Review, the basic operating principles, sunlight utilization, device architecture, reactor design, instantaneous and annually averaged solar-to-hydrogen (STH) conversion efficiency, and the operating conditions and constraints of both pathways are compared. A side-by-side comparison addresses some common sources of confusion and misinterpretation, especially in the evaluation of STH conversion efficiencies, and reveals distinct features and challenges in both PEC and STCH technologies. This Focus Review also addresses materials and device challenges in PEC and STCH for cost-competitive hydrogen generation.", "doi": "10.1021/acsenergylett.1c00758", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2021-09-10", "series_number": "9", "volume": "6", "issue": "9", "pages": "3096-3113" }, { "id": "authors:5abjc-d9v07", "collection": "authors", "collection_id": "5abjc-d9v07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210503-115704747", "type": "article", "title": "3D Printed Nickel\u2013Molybdenum-Based Electrocatalysts for Hydrogen Evolution at Low Overpotentials in a Flow-Through Configuration", "author": [ { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Zhang", "given_name": "Huanlei", "clpid": "Zhang-Huanlei" }, { "family_name": "Zhu", "given_name": "Cheng", "orcid": "0000-0003-0084-1099", "clpid": "Zhu-Cheng" }, { "family_name": "Wood", "given_name": "Marissa", "clpid": "Wood-Marissa" }, { "family_name": "Nelson", "given_name": "Art J.", "clpid": "Nelson-Art-J" }, { "family_name": "Baker", "given_name": "Sarah E.", "clpid": "Baker-Sarah-E" }, { "family_name": "Spadaccini", "given_name": "Christopher M.", "clpid": "Spadaccini-Christopher-M" }, { "family_name": "Van Buuren", "given_name": "Tony", "clpid": "Van-Buuren-Tony" }, { "family_name": "Lin", "given_name": "Meng", "orcid": "0000-0001-7785-749X", "clpid": "Lin-Meng" }, { "family_name": "Duoss", "given_name": "Eric B.", "clpid": "Duoss-Eric-B" }, { "family_name": "Liang", "given_name": "Siwei", "clpid": "Liang-Siwei" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Three-dimensional (3D) printed, hierarchically porous nickel molybdenum (NiMo) electrocatalysts were synthesized and evaluated in a flow-through configuration for the hydrogen evolution reaction (HER) in 1.0 M KOH(aq) in a simple electrochemical H-cell. 3D NiMo electrodes possess hierarchically porous structures because of the resol-based aerogel precursor, which generates superporous carbon aerogel as a catalyst support. Relative to a traditional planar electrode configuration, the flow-through configuration allowed efficient removal of the hydrogen bubbles from the catalyst surface, especially at high operating current densities, and significantly decreased the overpotentials required for HER. An analytical model that accounted for the electrokinetics of HER as well as the mass transport with or without the flow-through configuration was developed to quantitatively evaluate voltage losses associated with kinetic overpotentials and ohmic resistance due to bubble formation in the porous electrodes. The chemical composition, electrochemical surface area (ECSA), and roughness factor (RF) were also systematically studied to assess the electrocatalytic performance of the 3D printed, hierarchically porous NiMo electrodes. An ECSA of 25163 cm\u00b2 was obtained with the highly porous structures, and an average overpotential of 45 mV at 10 mA cm\u207b\u00b2 was achieved over 24 h by using the flow-through configuration. The flow-through configuration evaluated in the simple H-cell achieved high electrochemical accessible surface areas for electrochemical reactions and provided useful information for adaption of the porous electrodes in flow cells.", "doi": "10.1021/acsami.1c05648", "issn": "1944-8244", "publisher": "American Chemical Society", "publication": "ACS Applied Materials & Interfaces", "publication_date": "2021-05-05", "series_number": "17", "volume": "13", "issue": "17", "pages": "20260-20268" }, { "id": "authors:k42dq-dak69", "collection": "authors", "collection_id": "k42dq-dak69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210330-080727558", "type": "article", "title": "Comparative Technoeconomic Analysis of Renewable Generation of Methane Using Sunlight, Water, and Carbon Dioxide", "author": [ { "family_name": "Welch", "given_name": "Alex J.", "orcid": "0000-0003-2132-9617", "clpid": "Welch-Alex-J" }, { "family_name": "Digdaya", "given_name": "Ibadillah A.", "orcid": "0000-0001-7349-0934", "clpid": "Digdaya-Ibadillah-A" }, { "family_name": "Kent", "given_name": "Ron", "clpid": "Kent-Ron" }, { "family_name": "Ghougassian", "given_name": "Paul", "clpid": "Ghougassian-Paul" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Thirty-one percent of the primary energy consumed in the United States comes from the burning of natural gas, 70\u201390% of which is composed of methane (CH\u2084). Natural gas is recovered from onshore and offshore natural gas and oil wells and from coal beds. Currently, the United States has enough supply of dry natural gas to sustain current consumption for 92 years. Meanwhile, California consumes 2.14 MMcf (43.2 million tons) of natural gas per year, over a quarter of which is used to generate electric power and which provides approximately 40% of the electrical energy in the state. Because an extensive nationwide storage and distribution network already exists for natural gas, the development of renewable CH\u2084 could enable rapid and widespread distribution of zero-carbon energy services. Thus, for California to meet its renewable portfolio standard, that is, 60% renewable energy for electricity generation by 2030, and to conserve a limited resource, it is imperative to assess how to develop and deploy technologies for renewable generation of CH\u2084 in the next decade.", "doi": "10.1021/acsenergylett.1c00174", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2021-04-09", "series_number": "4", "volume": "6", "issue": "4", "pages": "1540-1549" }, { "id": "authors:0bsky-h8w32", "collection": "authors", "collection_id": "0bsky-h8w32", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210401-090557418", "type": "article", "title": "Modeling the electrochemical behavior and interfacial junction profiles of bipolar membranes at solar flux relevant operating current densities", "author": [ { "family_name": "Lin", "given_name": "Meng", "orcid": "0000-0001-7785-749X", "clpid": "Lin-Meng" }, { "family_name": "Digdaya", "given_name": "Ibadillah A.", "orcid": "0000-0001-7349-0934", "clpid": "Digdaya-Ibadillah-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A 1-dimensional, multi-physics model that accounts for the migration and diffusion of solution species, electrostatics, and chemical reactions, in particular water dissociation (WD), at bipolar membrane (BPM) interfaces was developed to study the electrochemical behavior of bipolar membranes (BPMs) at solar flux relevant operating current densities (tens of mA cm\u207b\u00b2). Significant partial current densities for WD were observed at BPM voltages much less than the equilibrium voltage, e.g., 59 mV \u00d7 \u0394pH from both experiments and modeling. The co-ion leakage across the BPM at pH differentials accounted for the early presence of the partial current density for WD. Two distinctive electric field dependent WD pathways, the un-catalyzed pathway and the catalyzed pathway, were quantitatively and parametrically studied to improve the turn-on potential of the BPM. The catalyzed pathway accounted for the majority of the partial current density for WD at low voltages, while the un-catalyzed pathway dominated the WD at relatively high voltages. Significant WD was observed only within the interfacial CL (<5 nm), in which a large electric field was present. To improve the electrochemical behavior and the turn-on potential of BPMs, the impacts of the pK_a of the immobilized WD catalysts, the electric-field dependent rate constant, the thickness of the catalyst layer and fixed charge density in BPMs on the partial current densities for WD were studied systematically. In addition, the electrochemical behavior and concentration profiles of BPMs in a buffered electrolyte were studied and contrasted with those in an un-buffered electrolyte from both modeling and experiments.", "doi": "10.1039/d1se00201e", "issn": "2398-4902", "publisher": "Royal Society of Chemistry", "publication": "Sustainable Energy and Fuels", "publication_date": "2021-04-07", "series_number": "7", "volume": "5", "issue": "7", "pages": "2149-2158" }, { "id": "authors:rx44x-m0n17", "collection": "authors", "collection_id": "rx44x-m0n17", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210325-120635278", "type": "article", "title": "Electrochemical carbon dioxide capture to close the carbon cycle", "author": [ { "family_name": "Sharifian", "given_name": "R.", "clpid": "Sharifian-Rezvan" }, { "family_name": "Wagterveld", "given_name": "R. M.", "orcid": "0000-0002-5334-1293", "clpid": "Wagterveld-R-Martijn" }, { "family_name": "Digdaya", "given_name": "I. A.", "orcid": "0000-0001-7349-0934", "clpid": "Digdaya-Ibadillah-A" }, { "family_name": "Xiang", "given_name": "C.", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Vermaas", "given_name": "D. A.", "orcid": "0000-0002-4705-6453", "clpid": "Vermaas-David-A" } ], "abstract": "Electrochemical CO\u2082 capture technologies are gaining attention due to their flexibility, their ability to address decentralized emissions (e.g., ocean and atmosphere) and their fit in an electrified industry. In the present work, recent progress made in electrochemical CO\u2082 capture is reviewed. The majority of these methods rely on the concept of \"pH-swing\" and the effect it has on the CO\u2082 hydration/dehydration equilibrium. Through a pH-swing, CO\u2082 can be captured and recovered by shifting the pH of a working fluid between acidic and basic pH. Such swing can be applied electrochemically through electrolysis, bipolar membrane electrodialysis, reversible redox reactions and capacitive deionization. In this review, we summarize main parameters governing these electrochemical pH-swing processes and put the concept in the framework of available worldwide capture technologies. We analyse the energy efficiency and consumption of such systems, and provide recommendations for further improvements. Although electrochemical CO\u2082 capture technologies are rather costly compared to the amine based capture, they can be particularly interesting if more affordable renewable electricity and materials (e.g., electrode and membranes) become widely available. Furthermore, electrochemical methods have the ability to (directly) convert the captured CO\u2082 to value added chemicals and fuels, and hence prepare for a fully electrified circular carbon economy.", "doi": "10.1039/d0ee03382k", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2021-02-01", "series_number": "2", "volume": "14", "issue": "2", "pages": "781-814" }, { "id": "authors:eb8q2-9fd59", "collection": "authors", "collection_id": "eb8q2-9fd59", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201110-121459166", "type": "article", "title": "Understanding Multi-Ion Transport Mechanisms in Bipolar Membranes", "author": [ { "family_name": "Bui", "given_name": "Justin C.", "orcid": "0000-0003-4525-957X", "clpid": "Bui-Justin-C" }, { "family_name": "Digdaya", "given_name": "Ibadillah", "orcid": "0000-0001-7349-0934", "clpid": "Digdaya-Ibadillah-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Bell", "given_name": "Alexis T.", "orcid": "0000-0002-5738-4645", "clpid": "Bell-Alexis-T" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-Adam-Z" } ], "abstract": "Bipolar membranes (BPMs) have the potential to become critical components in electrochemical devices for a variety of electrolysis and electrosynthesis applications. Because they can operate under large pH gradients, BPMs enable favorable environments for electrocatalysis at the individual electrodes. Critical to the implementation of BPMs in these devices is understanding the kinetics of water dissociation that occurs within the BPM as well as the co- and counter-ion crossover through the BPM, which both present significant obstacles to developing efficient and stable BPM-electrolyzers. In this study, a continuum model of multi-ion transport in a BPM is developed and fit to experimental data. Specifically, concentration profiles are determined for all ionic species, and the importance of a water-dissociation catalyst is demonstrated. The model describes internal concentration polarization and co- and counter-ion crossover in BPMs, determining the mode of transport for ions within the BPM and revealing the significance of salt-ion crossover when operated with pH gradients relevant to electrolysis and electrosynthesis. Finally, a sensitivity analysis reveals that the performance and lifetime of BPMs can be improved substantially by using of thinner dissociation catalysts, managing water transport, modulating the thickness of the individual layers in the BPM to control salt-ion crossover, and increasing the ion-exchange capacity of the ion-exchange layers in order to amplify the water-dissociation kinetics at the interface.", "doi": "10.1021/acsami.0c12686", "issn": "1944-8244", "publisher": "American Chemical Society", "publication": "ACS Applied Materials & Interfaces", "publication_date": "2020-11-25", "series_number": "47", "volume": "12", "issue": "47", "pages": "52509-52526" }, { "id": "authors:d9826-7xc92", "collection": "authors", "collection_id": "d9826-7xc92", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200730-073238681", "type": "article", "title": "Modeling the Performance of A Flow-Through Gas Diffusion Electrode for Electrochemical Reduction of CO or CO\u2082", "author": [ { "family_name": "Chen", "given_name": "Yikai", "orcid": "0000-0002-2955-9671", "clpid": "Chen-Yikai" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A flow-through gas diffusion electrode (GDE) consisting of agglomerate catalysts for CO or CO\u2082 reduction, gas channels for reactants, aqueous electrolytes for ionic transport, and metallic current collectors was simulated and evaluated using a numerical model. The geometric partial current densities and Faradaic Efficiencies (FE) for CH\u2084, C\u2082H\u2084 and H\u2082 generation in GDEs were calculated and compared to the behavior of analogous aqueous-based planar electrodes. The pH-dependent kinetics for CH\u2084 and C\u2082H\u2084 generation were used to represent the intrinsic catalytic characteristics for the agglomerate catalyst. The modeling indicated that relative to planar electrodes for either CO reduction (COR) or CO\u2082 reduction (CO\u2082R), substantial increases in electrochemical reduction rates and Faradaic efficiencies are expected when flow-through GDEs are used. The spatially resolved pH and reaction rates within the flow-through GDEs were also simulated for two different operating pHs, and the resulting transport losses were analyzed quantitatively. For CO\u2082 reduction, substantial loss of CO\u2082 via chemical reaction with the locally alkaline electrolyte was observed due to the increased pH in operating GDEs.", "doi": "10.1149/1945-7111/ab987a", "issn": "1945-7111", "publisher": "The Electrochemical Society", "publication": "Journal of The Electrochemical Society", "publication_date": "2020-11-11", "series_number": "11", "volume": "167", "issue": "11", "pages": "Art. No. 114503" }, { "id": "authors:bxhz8-wd706", "collection": "authors", "collection_id": "bxhz8-wd706", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200909-135831840", "type": "article", "title": "A direct coupled electrochemical system for capture and conversion of CO\u2082 from oceanwater", "author": [ { "family_name": "Digdaya", "given_name": "Ibadillah A.", "orcid": "0000-0001-7349-0934", "clpid": "Digdaya-Ibadillah-A" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Lin", "given_name": "Meng", "orcid": "0000-0001-7785-749X", "clpid": "Lin-Meng" }, { "family_name": "Han", "given_name": "Lihao", "orcid": "0000-0002-0452-3381", "clpid": "Han-Lihao" }, { "family_name": "Cheng", "given_name": "Wen-Hui", "orcid": "0000-0003-3233-4606", "clpid": "Cheng-Wen-Hui" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Capture and conversion of CO\u2082 from oceanwater can lead to net-negative emissions and can provide carbon source for synthetic fuels and chemical feedstocks at the gigaton per year scale. Here, we report a direct coupled, proof-of-concept electrochemical system that uses a bipolar membrane electrodialysis (BPMED) cell and a vapor-fed CO\u2082 reduction (CO\u2082R) cell to capture and convert CO\u2082 from oceanwater. The BPMED cell replaces the commonly used water-splitting reaction with one-electron, reversible redox couples at the electrodes and demonstrates the ability to capture CO\u2082 at an electrochemical energy consumption of 155.4\u2009kJ\u2009mol\u207b\u00b9 or 0.98 kWh kg\u207b\u00b9 of CO\u2082 and a CO\u2082 capture efficiency of 71%. The direct coupled, vapor-fed CO\u2082R cell yields a total Faradaic efficiency of up to 95% for electrochemical CO\u2082 reduction to CO. The proof-of-concept system provides a unique technological pathway for CO\u2082 capture and conversion from oceanwater with only electrochemical processes.", "doi": "10.1038/s41467-020-18232-y", "pmcid": "PMC7474062", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2020-09-04", "volume": "11", "pages": "Art. No. 4412" }, { "id": "authors:y5n4f-9b980", "collection": "authors", "collection_id": "y5n4f-9b980", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200626-103612366", "type": "article", "title": "Correlating Oxidation State and Surface Area to Activity from Operando Studies of Copper CO Electroreduction Catalysts in a Gas-fed Device", "author": [ { "family_name": "Lee", "given_name": "Soo Hong", "orcid": "0000-0002-2734-9654", "clpid": "Lee-Soo-Hong" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Larson", "given_name": "David M.", "orcid": "0000-0001-9634-9175", "clpid": "Larson-David-M" }, { "family_name": "Liu", "given_name": "Guiji", "orcid": "0000-0002-3943-4119", "clpid": "Liu-Guiji" }, { "family_name": "Toma", "given_name": "Francesca M.", "orcid": "0000-0003-2332-0798", "clpid": "Toma-Francesca-M" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Drisdell", "given_name": "Walter S.", "orcid": "0000-0002-8693-4562", "clpid": "Drisdell-Walter-S" } ], "abstract": "The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under realistic working conditions. Oxide-derived Cu catalysts exhibit a remarkable selectivity toward multicarbon products for the electrochemical CO reduction reaction (CORR), but the exact role of the oxide remains elusive for explaining the performance enhancements. Here, we used operando X-ray absorption spectroscopy (XAS) coupled with simultaneous measurements of the catalyst activity and selectivity by gas chromatography (GC) to study the relationship between oxidation states of Cu-based catalysts and the activity for ethylene (C\u2082H\u2084) production in a CO gas-fed cell. By utilizing a custom-built XAS cell, oxidation states of Cu catalysts can be probed in device-relevant settings and under high current densities (>80 mA cm\u207b\u00b2) for the CORR. By employing an electrochemical oxidation process, we found that the Cu oxidation states and specific ion species do not correlate with C\u2082H\u2084 production. The difference in the CORR activity is also investigated in relation to electrochemical surface area (ECSA) changes. While the hydrogen evolution reaction (HER) activity is positively correlated to the ECSA changes, the increased C\u2082H\u2084 activity is not proportional to the ECSA. Ex situ characterization from microscopic techniques suggests that the changes in the C\u2082H\u2084 activity and selectivity may arise from a morphological transformation that evolves into a more active structure. These comprehensive results give rise to the development of a cell regeneration method that can restore the performance of the Cu catalyst without cell disassembly. Our study establishes a basis for the rational design of highly active electrocatalysts for broad-range reactions in a gas-fed device.", "doi": "10.1021/acscatal.0c01670", "issn": "2155-5435", "publisher": "American Chemical Society", "publication": "ACS Catalysis", "publication_date": "2020-07-17", "series_number": "14", "volume": "10", "issue": "14", "pages": "8000-8011" }, { "id": "authors:pp53y-mvb03", "collection": "authors", "collection_id": "pp53y-mvb03", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191219-112734154", "type": "article", "title": "Practical challenges in the development of photoelectrochemical solar fuels production", "author": [ { "family_name": "Spitler", "given_name": "Mark T.", "orcid": "0000-0003-4153-989X", "clpid": "Spitler-Mark-T" }, { "family_name": "Modestino", "given_name": "Miguel A.", "orcid": "0000-0003-2100-7335", "clpid": "Modestino-Miguel-A" }, { "family_name": "Deutsch", "given_name": "Todd G.", "orcid": "0000-0001-6577-1226", "clpid": "Deutsch-Todd-G" }, { "family_name": "Xiang", "given_name": "Chengxiang X.", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Durrant", "given_name": "James R.", "orcid": "0000-0001-8353-7345", "clpid": "Durrant-James-R" }, { "family_name": "Esposito", "given_name": "Daniel V.", "orcid": "0000-0002-0550-801X", "clpid": "Esposito-Daniel-V" }, { "family_name": "Haussener", "given_name": "Sophia", "orcid": "0000-0002-3044-1662", "clpid": "Haussener-Sophia" }, { "family_name": "Maldonado", "given_name": "Stephen", "orcid": "0000-0002-2917-4851", "clpid": "Maldonado-Stephen" }, { "family_name": "Sharp", "given_name": "Ian D.", "orcid": "0000-0001-5238-7487", "clpid": "Sharp-Ian-D" }, { "family_name": "Parkinson", "given_name": "Bruce A.", "orcid": "0000-0002-8950-1922", "clpid": "Parkinson-Bruce-Alan" }, { "family_name": "Ginley", "given_name": "David S.", "clpid": "Ginlet-David-S" }, { "family_name": "Houle", "given_name": "Frances A.", "orcid": "0000-0001-5571-2548", "clpid": "Houle-Frances-A" }, { "family_name": "Hannappel", "given_name": "Thomas", "orcid": "0000-0002-6307-9831", "clpid": "Hannappel-Thomas" }, { "family_name": "Neale", "given_name": "Nathan R.", "orcid": "0000-0001-5654-1664", "clpid": "Neale-Nathan-R" }, { "family_name": "Nocera", "given_name": "Daniel G.", "orcid": "0000-0001-5055-320X", "clpid": "Nocera-Daniel-G" }, { "family_name": "McIntyre", "given_name": "Paul C.", "clpid": "McIntyre-Paul-C" } ], "abstract": "This article addresses the challenges presented by photoelectrochemical solar fuels technology in a discussion that begins with a functioning device and proceeds to the more fundamental science of its component parts. In this flow of discussion issues are addressed that frame the discussion for the next, increasingly more fundamental topic. The analysis begins with a discussion of the need for an analytical facility for confirmation of reported efficiencies of solar fuels device prototypes and then progressively narrows its scope to prototype design, the discovery of novel materials and the design of durable interfacial structures for fuels evolution. Molecular hydrogen will be considered first as the target fuel since many of the challenges with hydrogen production are general and applicable to the more complex CO\u2082 reduction, which will be treated as a supplementary subject.", "doi": "10.1039/c9se00869a", "issn": "2398-4902", "publisher": "Royal Society of Chemistry", "publication": "Sustainable Energy and Fuels", "publication_date": "2020-03-01", "series_number": "3", "volume": "4", "issue": "3", "pages": "985-995" }, { "id": "authors:qy9xr-bw259", "collection": "authors", "collection_id": "qy9xr-bw259", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200109-143243316", "type": "article", "title": "CO\u2082 Reduction to CO with 19% Efficiency in a Solar-Driven Gas Diffusion Electrode Flow Cell under Outdoor Solar Illumination", "author": [ { "family_name": "Cheng", "given_name": "Wen-Hui", "orcid": "0000-0003-3233-4606", "clpid": "Cheng-Wen-Hui" }, { "family_name": "Richter", "given_name": "Matthias H.", "orcid": "0000-0003-0091-2045", "clpid": "Richter-Matthias-H" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Larson", "given_name": "David M.", "clpid": "Larson-David-M" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Brunschwig", "given_name": "Bruce S.", "orcid": "0000-0002-6135-6727", "clpid": "Brunschwig-B-S" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "abstract": "Solar-driven reduction of carbon dioxide represents a carbon-neutral pathway for the synthesis of fuels and chemicals. We report here results for solar-driven CO\u2082 reduction using a gas diffusion electrode (GDE) directly powered by a photovoltaic cell. A GaInP/GaInAs/Ge triple-junction photovoltaic cell was used to power a reverse-assembled gas diffusion electrode employing a Ag nanoparticle catalyst layer. The device had a solar-to-CO energy conversion efficiency of 19.1% under simulated AM 1.5G illumination at 1 Sun. The use of a reverse-assembled GDE prevented transition from a wetted to a flooded catalyst bed and allowed the device to operate stably for >150 h with no loss in efficiency. Outdoor measurements were performed under ambient solar illumination in Pasadena, California, resulting in a peak solar-to-CO efficiency of 18.7% with a CO production rate of 47 mg\u00b7cm\u207b\u00b2 per day and a diurnal-averaged solar-to-fuel conversion efficiency of 5.8%.", "doi": "10.1021/acsenergylett.9b02576", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2020-02-14", "series_number": "2", "volume": "5", "issue": "2", "pages": "470-476" }, { "id": "authors:nf85a-2ng35", "collection": "authors", "collection_id": "nf85a-2ng35", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190920-113304665", "type": "article", "title": "A Hybrid Catalyst-Bonded Membrane Device for Electrochemical Carbon Monoxide Reduction at Different Relative Humidities", "author": [ { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Han", "given_name": "Lihao", "orcid": "0000-0002-0452-3381", "clpid": "Han-Lihao" }, { "family_name": "Lee", "given_name": "Soo Hong", "orcid": "0000-0002-2734-9654", "clpid": "Lee-Soo-Hong" }, { "family_name": "Lin", "given_name": "Meng", "orcid": "0000-0001-7785-749X", "clpid": "Lin-Meng" }, { "family_name": "Larson", "given_name": "David M.", "clpid": "Larson-D-M" }, { "family_name": "Drisdell", "given_name": "Walter S.", "orcid": "0000-0002-8693-4562", "clpid": "Drisdell-W-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A hybrid catalyst-bonded membrane device using gaseous reactants for a carbon monoxide reduction (COR) reaction in the cathode chamber, an aqueous electrolyte for an oxygen evolution reaction (OER) in the anode chamber, and an anion exchange membrane (AEM) for product separation was modeled, constructed, and tested. The Cu electrocatalyst was electrodeposited onto gas diffusion layers (GDLs) and was directly bonded to AEM by mechanical pressing in the hybrid device. The impacts of relative humidity at the cathode inlet on the selectivity and activity of COR were investigated by computational modeling and experimental methods. At a relative humidity of 30%, the Cu-based catalyst in the hybrid device exhibited a total operating current density of 87 mA cm\u207b\u00b2 with a \u22122.0 V vs Ag/AgCl reference electrode, a Faradaic efficiency (FE) for C\u2082H\u2084 generation of 32.6%, and an FE for a liquid-based carbon product of 42.6%. Significant improvements in the partial current densities for COR were observed in relation to planar electrodes or flooded gas diffusion electrodes (GDEs). In addition, a custom test bed was constructed to characterize the oxidation states of the Cu catalysts in real time along with product analysis though the backside of the GDLs via operando X-ray absorption (XAS) measurements.", "doi": "10.1021/acssuschemeng.9b04959", "issn": "2168-0485", "publisher": "American Chemical Society", "publication": "ACS Sustainable Chemistry & Engineering", "publication_date": "2019-10-21", "series_number": "20", "volume": "7", "issue": "20", "pages": "16964-16970" }, { "id": "authors:g2dzs-91y42", "collection": "authors", "collection_id": "g2dzs-91y42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190627-130708138", "type": "article", "title": "An Experimental- and Simulation-Based Evaluation on the CO_2 Utilization Efficiency in Aqueous-based Electrochemical CO_2 Reduction Reactors with Ion-Selective Membranes", "author": [ { "family_name": "Lin", "given_name": "Meng", "orcid": "0000-0001-7785-749X", "clpid": "Lin-Meng" }, { "family_name": "Han", "given_name": "Lihao", "orcid": "0000-0002-0452-3381", "clpid": "Han-Lihao" }, { "family_name": "Singh", "given_name": "Meenesh R.", "orcid": "0000-0002-3638-8866", "clpid": "Singh-M-R" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "The CO_2 utilization efficiency of three types of electrochemical CO2 reduction (CO_2R) reactors using different ion-selective membranes, including anion exchange membrane (AEM), cation exchange membrane (CEM), and bipolar membrane (BPM), was studied quantitively via both experimental and simulation methods. The operating current density of the CO_2R reactors was chosen to be between 10 \u2013 50 mA cm^(-2) to be relevant for solar-fuel devices with relatively low photon flux from sunlight. In the AEM based CO_2R reactor with a 6-electron per carbon CO_2R at the cathode surface, an upper limit of 14.4% for the CO_2 utilization efficiency was revealed by modeling and validated by experimental measurements in CO_2 saturated aqueous electrolytes without any buffer electrolyte. Improvements in CO_2 utilization efficiency were observed when additional buffer electrolyte was added into the aqueous solution, especially in solutions with low bicarbonate concentrations. The effects of the feed rate of the input CO_2 stream, the Faradaic Efficiency (FE) and the participating electron numbers of the cathode reaction on the CO_2 utilization efficiency was also studied in the AEM based CO_2R reactor. The CEM based CO_2R reactor exhibited low CO_2 utilization efficiency with re-circulation between the catholyte and the anolyte, and was unsustainable due to the cation depletion from the anolyte without any re-circulation. The BPM based CO_2R reactor operated continuously without a significant increase in the cell voltage and exhibited significantly higher CO_2 utilization efficiency, up to 61.4%, as compared to the AEM based CO_2R reactors. Diffusive CO_2 loss across the BPM resulted in relatively low CO_2 utilization efficiency at low operating current densities. Modeling and simulation also provided target BPM properties for higher CO_2 utilization efficiency and efficient cell operation.", "doi": "10.1021/acsaem.9b00986", "issn": "2574-0962", "publisher": "American Chemical Society", "publication": "ACS Applied Energy Materials", "publication_date": "2019-08-26", "series_number": "8", "volume": "2", "issue": "8", "pages": "5843-5850" }, { "id": "authors:0raf9-cy352", "collection": "authors", "collection_id": "0raf9-cy352", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190321-152633678", "type": "article", "title": "Decoupling H_2(g) and O_2(g) Production in Water Splitting by a Solar-Driven V^(3+/2)+(aq,H_2SO_4)|KOH(aq) Cell", "author": [ { "family_name": "Ho", "given_name": "Alec", "clpid": "Ho-Alec" }, { "family_name": "Zhou", "given_name": "Xinghao", "orcid": "0000-0001-9229-7670", "clpid": "Zhou-Xinghao" }, { "family_name": "Han", "given_name": "Lihao", "orcid": "0000-0002-0452-3381", "clpid": "Han-Lihao" }, { "family_name": "Sullivan", "given_name": "Ian", "orcid": "0000-0003-0632-4607", "clpid": "Sullivan-Ian" }, { "family_name": "Karp", "given_name": "Christoph", "clpid": "Karp-C-L" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A solar-driven V^(3+/2+)(aq,H_2SO_4)|KOH(aq) cell, consisting of a carbon-cloth cathode in 2.0 M H_2SO_4(aq) with 0.36 M V_2(SO_4)_3 (pH \u22120.16), a Ni mesh anode in 2.5 M KOH(aq) (pH 14.21) for the oxygen-evolution reaction (OER), and a bipolar membrane that sustained the pH differentials between the catholyte and anolyte, enabled water splitting with spatial and temporal decoupling of the hydrogen evolution reaction (HER) from the OER and produced H_2(g) locally under pressure upon demand. Over a range of potentials and charging depths, V^(3+) was selectively reduced with >99.8% faradic efficiency. The V^(2+) species produced in the catholyte was then passed subsequently on demand over a MoCx-based HER catalyst to produce H_2(g) and regenerate V^(3+) for subsequent reduction. Under a base hydrogen pressure of 1, 10, and 100 atm, the discharge efficiency of the V^(3+) to hydrogen was 83%, 65.2%, and 59.8%, respectively. In conjunction with a solar tracker and a photovoltaic device, the V^(3+/2+)(aq,H_2SO_4)|KOH(aq) cell was charged outdoors under sunlight and discharged at night with a daily averaged diurnal solar-to-hydrogen (STH) energy conversion efficiency of 3.7% and a STH conversion efficiency of 5.8% during daylight operation.", "doi": "10.1021/acsenergylett.9b00278", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2019-04-12", "series_number": "4", "volume": "4", "issue": "4", "pages": "968-976" }, { "id": "authors:mza73-yw131", "collection": "authors", "collection_id": "mza73-yw131", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181217-081303242", "type": "article", "title": "Gas-Diffusion Electrodes for Carbon-Dioxide Reduction: A New Paradigm", "author": [ { "family_name": "Higgins", "given_name": "Drew", "orcid": "0000-0002-0585-2670", "clpid": "Higgins-D-C" }, { "family_name": "Hahn", "given_name": "Christopher", "orcid": "0000-0002-2772-6341", "clpid": "Hahn-C" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Jaramillo", "given_name": "Thomas F.", "orcid": "0000-0001-9900-0622", "clpid": "Jaramillo-T-F" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-A-Z" } ], "abstract": "Significant advances have been made in recent years discovering new electrocatalysts and developing a fundamental understanding of electrochemical CO_2 reduction processes. This field has progressed to the point that efforts can now focus on translating this knowledge toward the development of practical CO_2 electrolyzers, which have the potential to replace conventional petrochemical processes as a sustainable route to produce fuels and chemicals. In this Perspective, we take a critical look at the progress in incorporating electrochemical CO_2 reduction catalysts into practical device architectures that operate using vapor-phase CO_2 reactants, thereby overcoming intrinsic limitations of aqueous-based systems. Performance comparison is made between state-of-the-art CO_2 electrolyzers and commercial H_2O electrolyzers\u2014a well-established technology that provides realistic performance targets. Beyond just higher rates, vapor-fed reactors represent new paradigms for unprecedented control of local reaction conditions, and we provide a perspective on the challenges and opportunities for generating fundamental knowledge and achieving technological progress toward the development of practical CO_2 electrolyzers.", "doi": "10.1021/acsenergylett.8b02035", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2019-01-11", "series_number": "1", "volume": "4", "issue": "1", "pages": "317-324" }, { "id": "authors:xjfy9-eva45", "collection": "authors", "collection_id": "xjfy9-eva45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180717-144513102", "type": "article", "title": "Comparative Analysis of Solar-to-Fuel Conversion Efficiency: A Direct, One-Step Electrochemical CO_2 Reduction Reactor versus a Two-Step, Cascade Electrochemical CO_2 Reduction Reactor", "author": [ { "family_name": "Zhou", "given_name": "Xinghao", "orcid": "0000-0001-9229-7670", "clpid": "Zhou-Xinghao" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Electrochemical and photoelectrochemical (PEC) CO_2 reduction (CO_2R) have the potential to produce sustainable, zero greenhouse gas emission fuels and chemicals. One of the key components in a PEC CO2 reduction device is the electrocatalyst materials for the CO_2R reaction. While significant research advances have been made in the development of CO_2 reduction catalysts and in the understanding of the reaction mechanisms, selective, active, and stable catalyst materials have yet to be identified to directly convert CO_2 into higher reduction products, such as ethanol and ethylene. In contrast, several electrocatalyst systems have exhibited promising selectivity and activity for the first two-electron, two-proton process, such as CO_2R to CO or formate. For example, nanostructured silver electrodes, metal dichalcogenides, and single metal atoms in graphene nanosheets exhibited high Faradaic efficiency (FE) and high reaction rates for CO_2R to CO. A Pd/C nanoparticle-based catalyst incorporated in a 10% efficient solar-to-formate conversion device also exhibited near-unity FE at 10s of mA cm^(\u20132) for CO_2R to formate. Hence, one alternative strategy is to leverage the efficient first two-electron, two-proton reaction by using a two-step, cascade CO_2 reactor, in which the first catalytic reactor converts CO_2 into CO or formate and the second catalytic reactor converts CO or formate into higher-order reduction products such as ethanol or ethylene. Herein, the solar-to-fuel (STF) conversion efficiencies in a direct, one-step CO2reduction reactor and a two-step, cascade CO_2 reduction reactor were analyzed and compared for two distinctive device configurations.", "doi": "10.1021/acsenergylett.8b01077", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2018-08-10", "series_number": "8", "volume": "3", "issue": "8", "pages": "1892-1897" }, { "id": "authors:72y3s-kga67", "collection": "authors", "collection_id": "72y3s-kga67", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180314-101126488", "type": "article", "title": "High Rate Electrochemical Reduction of Carbon Monoxide to Ethylene using Cu-Nanoparticle-Based Gas Diffusion Electrodes", "author": [ { "family_name": "Han", "given_name": "Lihao", "orcid": "0000-0002-0452-3381", "clpid": "Han-Lihao" }, { "family_name": "Zhou", "given_name": "Wuzong", "orcid": "0000-0001-9752-7076", "clpid": "Zhou-Wuzong" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "Gas diffusion electrodes (GDEs) with high electrochemically active surface areas (ECSAs) and triple-phase boundaries for efficient gas, electron, and ion transport offer a unique opportunity for high-rate electrochemical CO reduction (COR) in relative to traditional aqueous configurations. Cu-nanoparticle-based GDEs were fabricated by applying a mixture of carbon powders, copper acetate aqueous solution, and Teflon onto a Cu gauze substrate. The catalyst-coated substrate was air-dried, mechanically pressed, and subsequently annealed under forming gas to produce GDEs. Two distinctive types of GDE configurations, a flow-through configuration and a flow-by configuration, were constructed, characterized, and tested to quantitatively evaluate the effects of reactant gas transport on the activity and the selectivity of the GDE materials for COR. In the flow-through configuration, a high partial current density of 50.8 mA cm^(\u20132) for COR to C_2H_4 was achieved at \u22120.85 V vs RHE in 10 M KOH at \u221215 \u00b0C, while in the flow-by configuration with the same catalyst materials the partial current density for C_2H_4 generation was limited to <1 mA cm^(\u20132).", "doi": "10.1021/acsenergylett.8b00164", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2018-04-13", "series_number": "4", "volume": "3", "issue": "4", "pages": "855-860" }, { "id": "authors:s8mmt-5cj55", "collection": "authors", "collection_id": "s8mmt-5cj55", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180131-150900860", "type": "article", "title": "Effects of Electrolyte Buffer Capacity on Surface Reactant Species and Reaction Rate of CO_2 in Electrochemical CO_2 Reduction", "author": [ { "family_name": "Hashiba", "given_name": "Hiroshi", "clpid": "Hashiba-Hiroshi" }, { "family_name": "Weng", "given_name": "Lien-Chun", "clpid": "Weng-Lien-Chun" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Sato", "given_name": "Hiroki K.", "clpid": "Sato-Hiroki-K" }, { "family_name": "Yotsuhashi", "given_name": "Satoshi", "clpid": "Yotsuhashi-Satoshi" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-A-Z" } ], "abstract": "In the aqueous electrochemical reduction of CO_2, the choice of electrolyte is responsible for the catalytic activity and selectivity, although there remains a need for more in-depth understanding of electrolyte effects and mechanisms. In this study, using both experimental and simulation approaches, we report how the buffer capacity of the electrolytes affects the kinetics and equilibrium of surface reactant species and resulting reaction rate of CO_2 with varying partial CO_2 pressure. Electrolytes investigated include KCl (non-buffered), KHCO3 (buffered by bicarbonate), and phosphate buffered electrolytes. Assuming 100% methane production, the simulation successfully explains the experimental trends of maximum CO_2 flux in KCl and KHCO_3, and also highlights the difference between KHCO_3 and phosphate in terms of pKa as well as the impact of buffer capacity. To examine the electrolyte impact on selectivity, the model is run with a constant total current density. Using this model, several factors are elucidated including the importance of local pH, which is not in acid/base equilibrium, the impact of buffer identity and kinetics, and the mass-transport boundary-layer thickness. The gained understanding can help optimize CO_2 reduction in aqueous environments.", "doi": "10.1021/acs.jpcc.7b11316", "issn": "1932-7447", "publisher": "American Chemical Society", "publication": "Journal of Physical Chemistry C", "publication_date": "2018-02-22", "series_number": "7", "volume": "122", "issue": "7", "pages": "3719-3726" }, { "id": "authors:y85rf-07v48", "collection": "authors", "collection_id": "y85rf-07v48", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170627-075439064", "type": "article", "title": "Nanoelectrical and Nanoelectrochemical Imaging of Pt/p-Si and Pt/p+-Si Electrodes", "author": [ { "family_name": "Jiang", "given_name": "Jingjing", "clpid": "Jiang-Jingjing" }, { "family_name": "Huang", "given_name": "Zhuangqun", "clpid": "Huang-Zhuangqun" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Poddar", "given_name": "Rakesh", "clpid": "Poddar-R" }, { "family_name": "Lewerenz", "given_name": "Hans-Joachim", "orcid": "0000-0001-8433-9471", "clpid": "Lewerenz-H-J" }, { "family_name": "Papadantonakis", "given_name": "Kimberly M.", "orcid": "0000-0002-9900-5500", "clpid": "Papadantonakis-Kimberly-M" }, { "family_name": "Lewis", "given_name": "Nathan", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Brunschwig", "given_name": "Bruce", "orcid": "0000-0002-6135-6727", "clpid": "Brunschwig-B-S" } ], "abstract": "The interfacial properties of electrolessly deposited Pt nanoparticles (Pt-NP) on p-Si and p+-Si electrodes have been resolved on the nanometer scale using a combination of scanning probe methods. Atomic-force microscopy (AFM) showed highly dispersed Pt nanoparticles. Conductive AFM measurements showed that only about half of the particles exhibited measurable contact currents, with a factor of 10^3 difference in current. Local current-voltage measurements revealed a rectifying junction with a resistance of \u2265 10 M\u03a9 at the Pt-NP/p-Si interface, while Pt-NP/p+-Si samples formed an Ohmic junction with a local resistance of \u2265 1 M\u03a9. The particles were strongly attached to the sample surface in air. However in contact with an electrolyte, the adhesion of the particles to the surface was substantially lower. Scanning electrochemical microscopy (SECM) showed smaller, but more uniform electrochemical currents for the particles relative to the currents observed in conductive AFM measurements. In accord with the conductive AFM measurements, SECM measurements showed conductance through the substrate for only a minority of the particles. These results suggest that the electrochemical performance of the electrolessly deposited Pt nanoparticles on Si is ascribable to: 1) the high resistance of the contact between the particles and the substrate; 2) the low (<50%) fraction of particles that support high currents; and 3) the low adhesion of the particles to the surface in the electrolyte.", "doi": "10.1002/cssc.201700893", "issn": "1864-5631", "publisher": "Wiley", "publication": "ChemSusChem", "publication_date": "2017-11-23", "series_number": "22", "volume": "10", "issue": "22", "pages": "4657-4663" }, { "id": "authors:n5fa1-84d93", "collection": "authors", "collection_id": "n5fa1-84d93", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180914-100811320", "type": "article", "title": "Solar-Driven Reduction of 1 atm CO_2 to Formate at 10% Energy-Conversion Efficiency by Use of a TiO_2-Protected III-V Tandem Photoanode in Conjunction with a Bipolar Membrane and a Pd/C Cathode Electrocatalyst", "author": [ { "family_name": "Zhou", "given_name": "Xinghao", "orcid": "0000-0001-9229-7670", "clpid": "Zhou-Xinghao" }, { "family_name": "Liu", "given_name": "Rui", "clpid": "Liu-Rui" }, { "family_name": "Sun", "given_name": "Ke", "orcid": "0000-0001-8209-364X", "clpid": "Sun-Ke" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Verlage", "given_name": "Erik", "clpid": "Verlage-E" }, { "family_name": "Francis", "given_name": "Sonja A.", "clpid": "Francis-S-A" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A solar-driven CO_2-reduction (CO2R) cell, consisting of a tandem GaAs/InGaP/TiO_2/Ni photoanode in 1.0 M KOH(aq) (pH=13.7) to facilitate the oxygen-evolution reaction (OER), a Pd/C nanoparticle-coated Ti mesh cathode in 2.8 M KHCO_3(aq) (pH=8.0) to perform the CO_2R reaction, and a bipolar membrane to allow for steady-state operation of the catholyte and anolyte at different bulk pH values, was constructed. At the operational current density of 8.5 mA cm^(-2), in 2.8 M KHCO_3(aq), the cathode exhibited <100 mV overpotential and >94% Faradaic efficiency for the reduction of 1 atm of CO_2(g)to formate. The anode exhibited 320 \u00b1 7 mV overpotential for the OER in 1.0 M KOH(aq), and the bipolar membrane exhibited ~480 mV voltage loss with minimal product crossover as well as >90% and >95% selectivity for protons and hydroxide ions, respectively. The solar-driven CO_2R cell converted sunlight to fuels at an energy-conversion efficiency of ~10%.", "doi": "10.1149/07704.0031ecst", "issn": "1938-6737", "publisher": "Electrochemical Society", "publication": "ECS Transactions", "publication_date": "2017-05-20", "series_number": "4", "volume": "77", "issue": "4", "pages": "31-41" }, { "id": "authors:cejcq-j3821", "collection": "authors", "collection_id": "cejcq-j3821", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170317-120009870", "type": "article", "title": "Evaluation of flow schemes for near-neutral pH electrolytes in solar-fuel generators", "author": [ { "family_name": "Singh", "given_name": "Meenesh R.", "orcid": "0000-0002-3638-8866", "clpid": "Singh-M-R" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The electrochemical performance of three different types of membrane-containing electrolyte-flow schemes for solar-driven water splitting has been studied quantitatively using 1-dimensional and 2-dimensional multi-physics models. The three schemes include a recirculation scheme with a well-mixed bulk electrolyte, a recirculation scheme with laminar flow fields, and a fresh-feed scheme with laminar flow fields. The Nernstian potential loss associated with pH gradients at the electrode surfaces, the resistive loss between the cathode and anode, the product-gas crossovers, and the required pumping energy in all three schemes have been evaluated as a function of the operational current density, the flow rates for the electrolyte, and the physical dimensions of the devices. The trade-offs in the voltage loss, safety considerations, and energy inputs from the balance-of-systems required to produce a practical device have been evaluated and compared to membrane-free devices as well as to devices that operate at extreme pH values.", "doi": "10.1039/C7SE00062F", "issn": "2398-4902", "publisher": "Royal Society of Chemistry", "publication": "Sustainable Energy and Fuels", "publication_date": "2017-05-01", "series_number": "3", "volume": "1", "issue": "3", "pages": "458-466" }, { "id": "authors:j1j3v-qcr65", "collection": "authors", "collection_id": "j1j3v-qcr65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170131-095024118", "type": "article", "title": "Atomic force microscopy with nanoelectrode tips for high resolution electrochemical, nanoadhesion and nanoelectrical imaging", "author": [ { "family_name": "Nellist", "given_name": "Michael R.", "clpid": "Nellist-M-R" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Mark", "given_name": "Andreas", "clpid": "Mark-A" }, { "family_name": "G\u00f6drich", "given_name": "Sebastian", "clpid": "G\u00f6drich-S" }, { "family_name": "Stelling", "given_name": "Christian", "clpid": "Stelling-C" }, { "family_name": "Jiang", "given_name": "Jingjing", "clpid": "Jiang-Jingjing" }, { "family_name": "Poddar", "given_name": "Rakesh", "clpid": "Poddar-R" }, { "family_name": "Li", "given_name": "Chunzeng", "clpid": "Li-Chunzeng" }, { "family_name": "Kumar", "given_name": "Ravi", "clpid": "Kumar-R" }, { "family_name": "Papastavrou", "given_name": "Georg", "clpid": "Papastavrou-G" }, { "family_name": "Retsch", "given_name": "Markus", "clpid": "Retsch-M" }, { "family_name": "Brunschwig", "given_name": "Bruce S.", "orcid": "0000-0002-6135-6727", "clpid": "Brunschwig-B-S" }, { "family_name": "Huang", "given_name": "Zhuangqun", "clpid": "Huang-Zhuangqun" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Boettcher", "given_name": "Shannon W.", "orcid": "0000-0001-8971-9123", "clpid": "Boettcher-S-W" } ], "abstract": "Multimodal nano-imaging in electrochemical environments is important across many areas of science and technology. Here, scanning electrochemical microscopy (SECM) using an atomic force microscope (AFM) platform with a nanoelectrode probe is reported. In combination with PeakForce tapping AFM mode, the simultaneous characterization of surface topography, quantitative nanomechanics, nanoelectronic properties, and electrochemical activity is demonstrated. The nanoelectrode probe is coated with dielectric materials and has an exposed conical Pt tip apex of ~200 nm in height and of ~25 nm in end-tip radius. These characteristic dimensions permit sub-100 nm spatial resolution for electrochemical imaging. With this nanoelectrode probe we have extended AFM-based nanoelectrical measurements to liquid environments. Experimental data and numerical simulations are used to understand the response of the nanoelectrode probe. With PeakForce SECM, we successfully characterized a surface defect on a highly-oriented pyrolytic graphite electrode showing correlated topographical, electrochemical and nanomechanical information at the highest AFM-SECM resolution. The SECM nanoelectrode also enabled the measurement of heterogeneous electrical conductivity of electrode surfaces in liquid. These studies extend the basic understanding of heterogeneity on graphite/graphene surfaces for electrochemical applications.", "doi": "10.1088/1361-6528/aa5839", "issn": "0957-4484", "publisher": "IOP", "publication": "Nanotechnology", "publication_date": "2017-03-03", "series_number": "9", "volume": "28", "issue": "9", "pages": "Art. No. 095711" }, { "id": "authors:kdyj6-gva30", "collection": "authors", "collection_id": "kdyj6-gva30", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161003-141800305", "type": "article", "title": "Solar-Driven Reduction of 1 atm of CO_2 to Formate at 10% Energy-Conversion Efficiency by Use of a TiO_2-Protected III\u2013V Tandem Photoanode in Conjunction with a Bipolar Membrane and a Pd/C Cathode", "author": [ { "family_name": "Zhou", "given_name": "Xinghao", "orcid": "0000-0001-9229-7670", "clpid": "Zhou-Xinghao" }, { "family_name": "Liu", "given_name": "Rui", "clpid": "Liu-Rui" }, { "family_name": "Sun", "given_name": "Ke", "orcid": "0000-0001-8209-364X", "clpid": "Sun-Ke" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Verlage", "given_name": "Erik", "clpid": "Verlage-E" }, { "family_name": "Francis", "given_name": "Sonja A.", "clpid": "Francis-S-A" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A solar-driven CO_2 reduction (CO_2R) cell was constructed, consisting of a tandem GaAs/InGaP/TiO_2/Ni photoanode in 1.0 M KOH(aq) (pH = 13.7) to facilitate the oxygen-evolution reaction (OER), a Pd/C nanoparticle-coated Ti mesh cathode in 2.8 M KHCO_3(aq) (pH = 8.0) to perform the CO_2R reaction, and a bipolar membrane to allow for steady-state operation of the catholyte and anolyte at different bulk pH values. At the operational current density of 8.5 mA cm^(\u20132), in 2.8 M KHCO_3(aq), the cathode exhibited <100 mV overpotential and >94% Faradaic efficiency for the reduction of 1 atm of CO_2(g) to formate. The anode exhibited a 320 \u00b1 7 mV overpotential for the OER in 1.0 M KOH(aq), and the bipolar membrane exhibited \u223c480 mV voltage loss with minimal product crossovers and >90 and >95% selectivity for protons and hydroxide ions, respectively. The bipolar membrane facilitated coupling between two electrodes and electrolytes, one for the CO_2R reaction and one for the OER, that typically operate at mutually different pH values and produced a lower total cell overvoltage than known single-electrolyte CO_2R systems while exhibiting \u223c10% solar-to-fuels energy-conversion efficiency.", "doi": "10.1021/acsenergylett.6b00317", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2016-10-14", "series_number": "4", "volume": "1", "issue": "4", "pages": "764-770" }, { "id": "authors:rjc7h-j7y77", "collection": "authors", "collection_id": "rjc7h-j7y77", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160729-070531307", "type": "article", "title": "Modeling, Simulation, and Implementation of Solar-Driven Water-Splitting Devices", "author": [ { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-A-Z" }, { "family_name": "Ardo", "given_name": "Shane", "orcid": "0000-0001-7162-6826", "clpid": "Ardo-S" }, { "family_name": "Berger", "given_name": "Alan", "clpid": "Berger-A-D" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Coridan", "given_name": "Robert", "orcid": "0000-0003-1916-4446", "clpid": "Coridan-R-H" }, { "family_name": "Fountaine", "given_name": "Katherine T.", "orcid": "0000-0002-0414-8227", "clpid": "Fountaine-K-T" }, { "family_name": "Haussener", "given_name": "Sophia", "orcid": "0000-0002-3044-1662", "clpid": "Haussener-S" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" }, { "family_name": "Liu", "given_name": "Rui", "clpid": "Liu-Rui" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Modestino", "given_name": "Miguel A.", "orcid": "0000-0003-2100-7335", "clpid": "Modestino-M-A" }, { "family_name": "Shaner", "given_name": "Matthew M.", "orcid": "0000-0003-4682-9757", "clpid": "Shaner-M-R" }, { "family_name": "Singh", "given_name": "Meenesh R.", "orcid": "0000-0002-3638-8866", "clpid": "Singh-M-R" }, { "family_name": "Stevens", "given_name": "John C.", "clpid": "Stevens-J-C" }, { "family_name": "Sun", "given_name": "Ke", "orcid": "0000-0001-8209-364X", "clpid": "Sun-Ke" }, { "family_name": "Walczak", "given_name": "Karl", "clpid": "Walczak-K-A" } ], "abstract": "An integrated cell for the solar-driven splitting of water consists of multiple functional components and couples various photoelectrochemical (PEC) processes at different length and time scales. The overall solar-to-hydrogen (STH) conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as on the component integration, overall device architecture, and system operating conditions. This Review focuses on the modeling- and simulation-guided development and implementation of solar-driven water-splitting prototypes from a holistic viewpoint that explores the various interplays between the components. The underlying physics and interactions at the cell level is are reviewed and discussed, followed by an overview of the use of the cell model to provide target properties of materials and guide the design of a range of traditional and unique device architectures.", "doi": "10.1002/anie.201510463", "issn": "1433-7851", "publisher": "Wiley", "publication": "Angewandte Chemie International Edition", "publication_date": "2016-10-10", "series_number": "42", "volume": "55", "issue": "42", "pages": "12974-12988" }, { "id": "authors:ten2s-ypj95", "collection": "authors", "collection_id": "ten2s-ypj95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161128-081718603", "type": "article", "title": "Solar-Driven H_2O_2 Generation From H_2O and O_2 Using Earth-Abundant Mixed-Metal Oxide@Carbon Nitride Photocatalysts", "author": [ { "family_name": "Wang", "given_name": "Ruirui", "clpid": "Wang-Ruirui" }, { "family_name": "Pan", "given_name": "Kecheng", "clpid": "Pan-Kecheng" }, { "family_name": "Han", "given_name": "Dandan", "clpid": "Han-Dandan" }, { "family_name": "Jiang", "given_name": "Jingjing", "clpid": "Jiang-Jingjing" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Huang", "given_name": "Zhuangqun", "clpid": "Huang-Zhuangqun" }, { "family_name": "Zhang", "given_name": "Lu", "clpid": "Zhang-Lu" }, { "family_name": "Xiang", "given_name": "Xu", "clpid": "Xiang-Xu" } ], "abstract": "Light-driven generation of H_2O_2 only from water and molecular oxygen could be an ideal pathway for clean production of solar fuels. In this work, a mixed metal oxide/graphitic-C_3N_4 (MMO@C_3N_4) composite was synthesized as a dual-functional photocatalyst for both water oxidation and oxygen reduction to generate H_2O_2. The MMO was derived from a NiFe-layered double hydroxide (LDH) precursor for obtaining a high dispersion of metal oxides on the surface of the C_3N_4 matrix. The C_3N_4 is in the graphitic phase and the main crystalline phase in MMO is cubic NiO. The XPS analyses revealed the doping of Fe^(3+) in the dominant NiO phase and the existence of surface defects in the C3N4 matrix. The formation and decomposition kinetics of H_2O_2 on the MMO@C_3N_4 and the control samples, including bare MMO, C_3N_4 matrix, Ni- or Fe-loaded C_3N_4 and a simple mixture of MMO and C_3N_4, were investigated. The MMO@C_3N_4 composite produced 63 \u03bcmol\u2009L^(\u22121) of H_2O_2 in 90 min in acidic solution (pH 3) and exhibited a significantly higher rate of production for H_2O_2 relative to the control samples. The positive shift of the valence band in the composite and the enhanced water oxidation catalysis by incorporating the MMO improved the light-induced hole collection relative to the bare C_3N_4 and resulted in the enhanced H_2O_2 formation. The positively shifted conduction band in the composite also improved the selectivity of the two-electron reduction of molecular oxygen to H_2O_2.", "doi": "10.1002/cssc.201600705", "issn": "1864-5631", "publisher": "Wiley", "publication": "ChemSusChem", "publication_date": "2016-09-08", "series_number": "17", "volume": "9", "issue": "17", "pages": "2470-2479" }, { "id": "authors:6p4gf-1f651", "collection": "authors", "collection_id": "6p4gf-1f651", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160502-135457387", "type": "article", "title": "A Stabilized, Intrinsically Safe, 10% Efficient, Solar-Driven Water-Splitting Cell Incorporating Earth-Abundant Electrocatalysts with Steady-State pH Gradients and Product Separation Enabled by a Bipolar Membrane", "author": [ { "family_name": "Sun", "given_name": "Ke", "orcid": "0000-0001-8209-364X", "clpid": "Sun-Ke" }, { "family_name": "Liu", "given_name": "Rui", "clpid": "Liu-Rui" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Verlage", "given_name": "Erik", "clpid": "Verlage-E" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "An efficient, stable, and intrinsically safe solar water-splitting device is demonstrated using a III\u2013V tandem junction photoanode, an acid-stable, earth-abundant hydrogen evolution catalyst, and a bipolar membrane. The integrated photoelectrochemical cell operates under a steady-state pH gradient and achieves \u224810% solar-to-hydrogen conversion efficiency, >100 h of stability in a large (>1 cm^2) photoactive area in relation to most previous reports.", "doi": "10.1002/aenm.201600379", "issn": "1614-6832", "publisher": "Wiley", "publication": "Advanced Energy Materials", "publication_date": "2016-07-06", "series_number": "13", "volume": "6", "issue": "13", "pages": "Art. No. 1600379" }, { "id": "authors:s88pb-v4372", "collection": "authors", "collection_id": "s88pb-v4372", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160627-135527397", "type": "article", "title": "Modeling and Simulation of the Spatial and Light-Intensity Dependence of Product Distributions in an Integrated Photoelectrochemical CO_2 Reduction System", "author": [ { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A multiphysics model that accounts for the performance of electrocatalysts and triple-junction light absorbers, as well as for the transport properties of the electrolyte and dissolved CO_2, was used to evaluate the spatial and light-intensity dependence of product distributions in an integrated photoelectrochemical CO2 reduction (CO_2R) cell. Different sets of band gap combinations of triple-junction light absorbers were required to accommodate the optimal total operating current density relative to the optimal partial current density for CO_2R. The simulated product distribution was highly nonuniform along the width of the electrode and depended on the electrode dimensions as well as the illumination intensity. To achieve the same product selectivity as in a potentiostatic, \"half-cell\" configuration, the electrocatalyst must retain its selectivity over a range of cathode potentials, and this range is dependent on the transport losses and current\u2013voltage relationship of the light absorbers, the geometric parameters of the cell, and the illumination intensity.", "doi": "10.1021/acsenergylett.6b00134", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2016-06-08", "series_number": "1", "volume": "2016", "issue": "1", "pages": "273-280" }, { "id": "authors:31ctk-1hg50", "collection": "authors", "collection_id": "31ctk-1hg50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160307-084720706", "type": "article", "title": "Principles and implementations of electrolysis systems for water splitting", "author": [ { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Papadantonakis", "given_name": "Kimberly M.", "orcid": "0000-0002-9900-5500", "clpid": "Papadantonakis-Kimberly-M" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "Efforts to develop renewable sources of carbon-neutral fuels have brought a renewed focus to research and development of sunlight-driven water-splitting systems. Electrolysis of water to produce H_2 and O_2 gases is the foundation of such systems, is conceptually and practically simple, and has been practiced both in the laboratory and industrially for many decades. In this Focus article, we present the fundamentals of water splitting and describe practices which distinguish commercial water-electrolysis systems from simple laboratory-scale demonstrations.", "doi": "10.1039/c6mh00016a", "issn": "2051-6347", "publisher": "Royal Society of Chemistry", "publication": "Materials Horizons", "publication_date": "2016-05-01", "series_number": "3", "volume": "2016", "issue": "3", "pages": "169-173" }, { "id": "authors:9kdtn-8n505", "collection": "authors", "collection_id": "9kdtn-8n505", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151102-111406745", "type": "article", "title": "Operational constraints and strategies for systems to effect the sustainable, solar-driven reduction of atmospheric CO_2", "author": [ { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "The operational constraints for a 6-electron/6-proton CO_2 reduction system that operates at the concentration of CO_2 in the current atmosphere (p_(CO_2) = 400 ppm) have been evaluated on a variety of scale lengths that span from laboratory scale to global scale. Due to the low concentration of CO_2 in the atmosphere, limitations due to mass transport of CO_2 from the tropopause have been evaluated through five different regions, each with different characteristic length scales: the troposphere; the atmospheric boundary layer (ABL); the canopy layer; a membrane layer; and an aqueous electrolyte layer. The resulting CO_2 conductances, and associated physical transport limitations, will set the ultimate limit on the efficiency and areal requirements of a sustainable solar-driven CO_2 reduction system regardless of the activity or selectivity of catalysts for reduction of CO_2 at the molecular level. At the electrolyte/electrode interface, the steady-state limiting current density and the concomitant voltage loss associated with the CO_2 concentration overpotential in a one-dimensional solar-driven CO_2 reduction cell have been assessed quantitatively using a mathematical model that accounts for diffusion, migration and convective transport, as well as for bulk electrochemical reactions in the electrolyte. At p_(CO_2) = 400 ppm, the low diffusion coefficient combined with the low solubility of CO_2 in aqueous solutions constrains the steady-state limiting current density to <0.1 mA cm\u22122 in a typical electrochemical cell with natural convection and employing electrolytes with a range of pH values. Hence, in such a system, the CO_2 capture area must be 100- to 1000-fold larger than the solar photon collection area to enable a >10% efficient solar-driven CO_2 reduction system (based on the solar collection area). This flux limitation is consistent with estimates of oceanic CO_2 uptake fluxes that have been developed in conjunction with carbon-cycle analyses for use in coupled atmosphere/ocean general circulation models. Two strategies to improve the feasibility of obtaining efficient and sustainable CO_2 transport to a cathode surface at p_(CO_2) = 400 ppm are described and modeled quantitatively. The first strategy employs yet unknown catalysts, analogous to carbonic anhydrases, that dramatically accelerate the chemically enhanced CO_2 transport in the aqueous electrolyte layer by enhancing the acid\u2013base reactions in a bicarbonate buffer system. The rapid interconversion from bicarbonate to CO_2 in the presence of such catalysts near the cathode surface would in principle yield significant increases in the steady-state limiting current density and allow for >10% solar-fuel operation at the cell level. The second strategy employs a thin-layer cell architecture to improve the diffusive transport of CO_2 by use of an ultrathin polymeric membrane electrolyte. Rapid equilibration of CO_2 at the gas/electrolyte interface, and significantly enhanced diffusive fluxes of CO_2 in electrolytes, are required to increase the steady-state limiting current density of such a system. This latter approach however only is feasible for gaseous products, because liquid products would coat the electrode and therefore thicken the hydrodynamic boundary layer and accordingly reduce the diffusive CO_2 flux to the electrode surface. Regardless of whether the limitations due to mass transport to the electrode surface are overcome on the laboratory scale, at global scales the ultimate CO_2 flux limitations will be dictated by mass transport considerations related to transport of atmospheric CO_2 to the boundary plane of the solar-driven reactor system. The transport of CO_2 across the troposphere/ABL interface, the ABL/canopy layer interface, and the canopy layer/electrolyte interface have therefore been assessed in this work, to provide upper bounds on the ultimate limits for the solar-to-fuel (STF) conversion efficiency for systems that are intended to effect the reduction of atmospheric CO_2 in a sustainable fashion at global scale.", "doi": "10.1039/c5ee02908b", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2015-12", "series_number": "12", "volume": "8", "issue": "12", "pages": "3663-3674" }, { "id": "authors:rc1cc-r8722", "collection": "authors", "collection_id": "rc1cc-r8722", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150825-164619530", "type": "article", "title": "A Monolithically Integrated, Intrinsically Safe, 10% Efficient, Solar-Driven Water-Splitting System Based on Active, Stable Earth-Abundant Electrocatalysts in Conjunction with Tandem III-V Light Absorbers Protected by Amorphous TiO_2 Films", "author": [ { "family_name": "Verlage", "given_name": "Erik", "clpid": "Verlage-E" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" }, { "family_name": "Liu", "given_name": "Rui", "clpid": "Liu-Rui" }, { "family_name": "Jones", "given_name": "Ryan J. R.", "orcid": "0000-0002-4629-3115", "clpid": "Jones-R-J-R" }, { "family_name": "Sun", "given_name": "Ke", "orcid": "0000-0001-8209-364X", "clpid": "Sun-Ke" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lewis", "given_name": "Nathan", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Atwater", "given_name": "Harry A., Jr.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "abstract": "A monolithically integrated device consisting of a tandem-junction GaAs/InGaP photoanode coated by an amorphous TiO_2 stabilization layer, in conjunction with Ni-based, earth-abundant active electrocatalysts for the hydrogen-evolution and oxygen-evolution reactions, was used to effect unassisted, solar-driven water splitting in 1.0 M KOH(aq). When connected to a Ni-Mo-coated counterelectrode in a two-electrode cell configuration, the TiO_2-protected III-V tandem device exhibited a solar-to-hydrogen conversion efficiency, \u03b7_(STH), of 10.5% under 1 sun illumination, with stable performance for > 40 h of continuous operation at an efficiency of \u03b7_(STH) >10%. The protected tandem device also formed the basis for a monolithically integrated, intrinsically safe solar-hydrogen prototype system (1 cm^2) driven by a NiMo/GaAs/InGaP/TiO_2/Ni structure. The intrinsically safe system exhibited a hydrogen production rate of 0.81 \u03bcL s^(-1) and a solar-to-hydrogen conversion efficiency of 8.6% under 1 sun illumination in 1.0 M KOH(aq), with minimal product gas crossover while allowing for beneficial collection of separate streams of H_2(g) and O_2(g).", "doi": "10.1039/C5EE01786F", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2015-11-01", "series_number": "11", "volume": "8", "issue": "11", "pages": "3166-3172" }, { "id": "authors:0w1et-cwv76", "collection": "authors", "collection_id": "0w1et-cwv76", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150918-153945062", "type": "article", "title": "An electrochemical engineering assessment of the operational conditions and constraints for solar-driven water-splitting systems at near-neutral pH", "author": [ { "family_name": "Singh", "given_name": "Meenesh R.", "orcid": "0000-0002-3638-8866", "clpid": "Singh-M-R" }, { "family_name": "Papadantonakis", "given_name": "Kimberly M.", "orcid": "0000-0002-9900-5500", "clpid": "Papadantonakis-Kimberly-M" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The solution transport losses in a one-dimensional solar-driven water-splitting cell that operates in either concentrated acid, dilute acid, or buffered near-neutral pH electrolytes have been evaluated using a mathematical model that accounts for diffusion, migration and convective transport, as well as for bulk electrochemical reactions in the electrolyte. The Ohmic resistance loss, the Nernstian potential loss associated with pH gradients at the surface of the electrode, and electrodialysis in different electrolytes were assessed quantitatively in a stagnant cell as well as in a bubble-convected cell, in which convective mixing occurred due to product-gas evolution. In a stagnant cell that did not have convective mixing, small limiting current densities (<3 mA cm^(\u22122)) and significant polarization losses derived from pH gradients were present in dilute acid as well as in near-neutral pH buffered electrolytes. In contrast, bubble-convected cells exhibited a significant increase in the limiting current density, and a significant reduction of the concentration overpotentials. In a bubble-convected cell, minimal solution transport losses were present in membrane-free cells, in either buffered electrolytes or in unbuffered solutions with pH \u2264 1. However, membrane-free cells lack a mechanism for product-gas separation, presenting significant practical and engineering impediments to the deployment of such systems. To produce an intrinsically safe cell, an ion-exchange membrane was incorporated into the cell. The accompanying solution losses, especially the pH gradients at the electrode surfaces, were modeled and simulated for such a system. Hence this work describes the general conditions under which intrinsically safe, efficient solar-driven water-splitting cells can be operated.", "doi": "10.1039/c5ee01721a", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2015-09-01", "series_number": "9", "volume": "8", "issue": "9", "pages": "2760-2767" }, { "id": "authors:c5k1s-m1z53", "collection": "authors", "collection_id": "c5k1s-m1z53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150427-134904440", "type": "article", "title": "A quantitative analysis of the efficiency of solar-driven water-splitting device designs based on tandem photoabsorbers patterned with islands of metallic electrocatalysts", "author": [ { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Sun", "given_name": "Ke", "orcid": "0000-0001-8209-364X", "clpid": "Sun-Ke" }, { "family_name": "Audesirk", "given_name": "Heather A.", "clpid": "Audesirk-H-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The trade-off between the optical obscuration and kinetic overpotentials of electrocatalyst films patterned onto the surface of tandem light-absorber structures in model photoelectrosynthetic water-splitting systems was investigated using a 0-dimensional load-line analysis and experimental measurements. The electrocatalytic performance of the catalyst at high current densities, normalized to the electrocatalyst surface area, is an important factor in the dependence of the optimal solar-to-hydrogen (STH) conversion efficiency, \u03b7_(STH,opt), on the filling fraction (f_c) of the patterned catalysts, because even under conditions that produce minority-carrier current densities of ~10 mA cm^(\u22122) at the solid/liquid interface, the current density at catalyst-bearing sites can be >1\u20132 A cm^(\u22122) in low filling-fraction films. A universal current-density versus potential relationship, up to current densities of 10 A cm^(\u22122), was obtained experimentally for the hydrogen-evolution reaction (HER) using patterned Pt ultramicroelectrode (UME) arrays with a range of filling fractions and disc diameters. The \u03b7_(STH,opt) of system designs that utilize patterned electrocatalysts located on the illuminated side of tandem photoabsorbers was then evaluated systematically. The maximum STH conversion efficiency, \u03b7_(STH,max), using a hypothetical electrocatalyst that was optically transparent but which nevertheless exhibited a current-density versus potential behavior that is characteristic of the most active Pt films measured experimentally regardless of their optical obscuration, was 26.7%. By comparison, the maximum \u03b7_(STH,opt) of 24.9% for real patterned Pt electrocatalyst films closely approached this ideal-case limit. The performance and materials utilization of the patterned electrocatalysts and of the uniformly coated electrocatalysts on tandem photoabsorbers were also compared in this study. Hence, patterned electrocatalysts with very low filling fractions can provide a potentially promising path to the realization of efficient large-scale photoelectrolysis systems while minimizing the use of scarce noble metals.", "doi": "10.1039/c5ee00311c", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2015-06-01", "series_number": "6", "volume": "8", "issue": "6", "pages": "1736-1747" }, { "id": "authors:cp2rh-mc727", "collection": "authors", "collection_id": "cp2rh-mc727", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150430-084157336", "type": "article", "title": "A sensitivity analysis to assess the relative importance of improvements in electrocatalysts, light absorbers, and system geometry on the efficiency of solar-fuels generators", "author": [ { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "A sensitivity analysis has been performed for a variety of generic designs for solar-fuels generators. The analysis has revealed the relative importance of reductions in the overpotentials of electrocatalysts, of improvements in the materials properties of light absorbers, and of optimization in the system geometry for various different types of solar-fuels generators, while considering operation at a range of temperatures as well as under a variety of illumination intensities including up to 10-fold optical concentration.", "doi": "10.1039/c4ee02314e", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2015-03-01", "series_number": "3", "volume": "8", "issue": "3", "pages": "876-886" }, { "id": "authors:3ftp2-am278", "collection": "authors", "collection_id": "3ftp2-am278", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150422-095105837", "type": "article", "title": "Enabling solar fuels technology by high throughput discovery of earth abundant oxygen evolution reaction catalysts", "author": [ { "family_name": "Haber", "given_name": "Joel", "orcid": "0000-0001-7847-5506", "clpid": "Haber-J-A" }, { "family_name": "Guevarra", "given_name": "Dan", "orcid": "0000-0002-9592-3195", "clpid": "Guevarra-D-W" }, { "family_name": "Jones", "given_name": "Ryan", "orcid": "0000-0002-4629-3115", "clpid": "Jones-R-J-R" }, { "family_name": "Shinde", "given_name": "Aniketa", "orcid": "0000-0003-2386-3848", "clpid": "Shinde-A" }, { "family_name": "Becerra", "given_name": "Natalie", "clpid": "Becerra-Stasiewicz-N" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Mitrovic", "given_name": "Slobodan", "orcid": "0000-0001-8913-8505", "clpid": "Mitrovic-S" }, { "family_name": "Jung", "given_name": "Suho", "orcid": "0000-0002-8119-3902", "clpid": "Jung-Suho" }, { "family_name": "Kisielowski", "given_name": "Christian", "orcid": "0000-0001-6425-0779", "clpid": "Kisielowski-C" }, { "family_name": "Yano", "given_name": "Junko", "orcid": "0000-0001-6308-9071", "clpid": "Yano-Junko" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Gregoire", "given_name": "John", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "abstract": "The High Throughput Experimentation (HTE) project of the Joint Center for Artificial Photosynthesis performs accelerated\ndiscovery of new earth- abundant photoabsorbers and electrocatalysts. We will describe several new screening instruments\nfor high throughput (photo- ) electrochem. measurements and summarize the discovery pipelines. This approach will be\nillustrated using the high throughput discovery, follow- on verification, and device implementation of a new quaternary metal\noxide catalyst. Discovering improved electrocatalysts for the oxygen evolution reaction (OER) is of great importance for\nefficient solar fuels generation, regenerative fuel cells, and recharging metal air batteries. We report a new Ce- rich family of\nactive catalysts composed of earth abundant elements, which was discovered using high- throughput methods to produce\n5456 discrete compns. in the (Ni- Fe- Co- Ce) Ox compn. space. The activity and stability of this new OER catalyst was verified by\nre- synthesis and extensive electrochem. testing of samples in a std. format in 1.0 M NaOH. Characterization of selected\ncompns. by XRD, XPS, SEM, TEM, EDS, XRF mapping, and EXAFS both as- synthesized and after electrochem. testing, reveal the\nimportance of nanostructure to the obsd. electrochem. performance. The discovery of addnl. electrocatalysts by expansion of\nthe compn. space investigated and of new compn. spaces tested for OER activity and stability under acidic conditions will be\nreported.", "issn": "0065-7727", "publisher": "American Chemical Society", "publication": "Abstracts of Papers of the American Chemical Society", "publication_date": "2015-03", "volume": "249", "pages": "INOR-45" }, { "id": "authors:zx5dk-ap869", "collection": "authors", "collection_id": "zx5dk-ap869", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150310-113150374", "type": "article", "title": "Modeling, Simulation, and Fabrication of a Fully Integrated, Acid-stable, Scalable Solar-Driven Water-Splitting System", "author": [ { "family_name": "Walczak", "given_name": "Karl", "clpid": "Walczak-K-A" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Karp", "given_name": "Christoph", "clpid": "Karp-C-L" }, { "family_name": "Beeman", "given_name": "Jeffrey W.", "clpid": "Beeman-J-W" }, { "family_name": "Shaner", "given_name": "Matthew", "orcid": "0000-0003-4682-9757", "clpid": "Shaner-M-R" }, { "family_name": "Spurgeon", "given_name": "Joshua M.", "orcid": "0000-0002-2987-0865", "clpid": "Spurgeon-J-M" }, { "family_name": "Sharp", "given_name": "Ian D.", "orcid": "0000-0001-5238-7487", "clpid": "Sharp-I-D" }, { "family_name": "Amashukeli", "given_name": "Xenia", "clpid": "Amashukeli-X" }, { "family_name": "West", "given_name": "William", "clpid": "West-W-C" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "A fully integrated solar-driven water-splitting system comprised of WO3/FTO/p^(+)n Si as the photoanode, Pt/TiO_2/Ti/n^(+)p Si as the photocathode, and Nafion as the membrane separator, was simulated, assembled, operated in 1.0\u2009M HClO_4, and evaluated for performance and safety characteristics under dual side illumination. A multi-physics model that accounted for the performance of the photoabsorbers and electrocatalysts, ion transport in the solution electrolyte, and gaseous product crossover was first used to define the optimal geometric design space for the system. The photoelectrodes and the membrane separators were then interconnected in a louvered design system configuration, for which the light-absorbing area and the solution-transport pathways were simultaneously optimized. The performance of the photocathode and the photoanode were separately evaluated in a traditional three-electrode photoelectrochemical cell configuration. The photocathode and photoanode were then assembled back-to-back in a tandem configuration to provide sufficient photovoltage to sustain solar-driven unassisted water-splitting. The current\u2013voltage characteristics of the photoelectrodes showed that the low photocurrent density of the photoanode limited the overall solar-to-hydrogen (STH) conversion efficiency due to the large band gap of WO_3. A hydrogen-production rate of 0.17\u2005mL\u2009hr^\u22121 and a STH conversion efficiency of 0.24\u2009% was observed in a full cell configuration for >20\u2005h with minimal product crossover in the fully operational, intrinsically safe, solar-driven water-splitting system. The solar-to-hydrogen conversion efficiency, \u03b7S_TH, calculated using the multiphysics numerical simulation was in excellent agreement with the experimental behavior of the system. The value of \u03b7STH was entirely limited by the performance of the photoelectrochemical assemblies employed in this study. The louvered design provides a robust platform for implementation of various types of photoelectrochemical assemblies, and can provide an approach to significantly higher solar conversion efficiencies as new and improved materials become available.", "doi": "10.1002/cssc.201402896", "issn": "1864-5631", "publisher": "Wiley", "publication": "ChemSusChem", "publication_date": "2015-02", "series_number": "3", "volume": "8", "issue": "3", "pages": "544-551" }, { "id": "authors:xdf2h-1wk64", "collection": "authors", "collection_id": "xdf2h-1wk64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150126-085330620", "type": "article", "title": "Parallel Electrochemical Treatment System and Application for Identifying Acid-Stable Oxygen Evolution Electrocatalysts", "author": [ { "family_name": "Jones", "given_name": "Ryan J. R.", "orcid": "0000-0002-4629-3115", "clpid": "Jones-R-J-R" }, { "family_name": "Shinde", "given_name": "Aniketa", "orcid": "0000-0003-2386-3848", "clpid": "Shinde-A" }, { "family_name": "Guevarra", "given_name": "Dan", "orcid": "0000-0002-9592-3195", "clpid": "Guevarra-D-W" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Haber", "given_name": "Joel A.", "orcid": "0000-0001-7847-5506", "clpid": "Haber-J-A" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "abstract": "Many energy technologies require electrochemical stability or preactivation of functional materials. Due to the long experiment duration required for either electrochemical preactivation or evaluation of operational stability, parallel screening is required to enable high throughput experimentation. Imposing operational electrochemical conditions to a library of materials in parallel creates several opportunities for experimental artifacts. We discuss the electrochemical engineering principles and operational parameters that mitigate artifacts in the parallel electrochemical treatment system. We also demonstrate the effects of resistive losses within the planar working electrode through a combination of finite element modeling and illustrative experiments. Operation of the parallel-plate, membrane-separated electrochemical treatment system is demonstrated by exposing a composition library of mixed-metal oxides to oxygen evolution conditions in 1 M sulfuric acid for 2 h. This application is particularly important because the electrolysis and photoelectrolysis of water are promising future energy technologies inhibited by the lack of highly active, acid-stable catalysts containing only earth abundant elements.", "doi": "10.1021/co500148p", "issn": "2156-8952", "publisher": "American Chemical Society", "publication": "ACS Combinatorial Science", "publication_date": "2015-02", "series_number": "2", "volume": "17", "issue": "2", "pages": "71-75" }, { "id": "authors:4p0aq-va764", "collection": "authors", "collection_id": "4p0aq-va764", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140820-110452543", "type": "article", "title": "An experimental and modeling/simulation-based evaluation of the efficiency and operational performance characteristics of an integrated, membrane-free, neutral pH solar-driven water-splitting system", "author": [ { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Walczak", "given_name": "Karl", "clpid": "Walczak-K" }, { "family_name": "Singh", "given_name": "Meenesh R.", "orcid": "0000-0002-3638-8866", "clpid": "Singh-M-R" }, { "family_name": "Karp", "given_name": "Chris", "clpid": "Karp-C" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" } ], "abstract": "The efficiency limits, gas-crossover behavior, formation of local pH gradients near the electrode surfaces, and safety characteristics have been evaluated experimentally as well as by use of multi-physics modeling and simulation methods for an integrated solar-driven water-splitting system that operates with bulk electrolyte solutions buffered at near-neutral pH. The integrated membrane-free system utilized a triple-junction amorphous hydrogenated Si (a-Si:H) cell as the light absorber, Pt and cobalt phosphate (Co\u2013Pi) as electrocatalysts for the hydrogen-evolution reaction (HER) and oxygen-evolution reaction (OER), respectively, and a bulk aqueous solution buffered at pH = 9.2 by 1.0 M of boric acid/borate as an electrolyte. Although the solar-to-electrical efficiency of the stand-alone triple-junction a-Si:H photovoltaic cell was 7.7%, the solar-to-hydrogen (STH) conversion efficiency for the integrated membrane-free water-splitting system was limited under steady-state operation to 3.2%, and the formation of pH gradients near the electrode surfaces accounted for the largest voltage loss. The membrane-free system exhibited negligible product-recombination loss while operating at current densities near 3.0 mA cm^(\u22122), but exhibited significant crossover of products (up to 40% H_2 in the O_2 chamber), indicating that the system was not intrinsically safe. A system that contained a membrane to minimize the gas crossover, but which was otherwise identical to the membrane-free system, yielded very low energy-conversion efficiencies at steady state, due to low transference numbers for protons across the membranes resulting in electrodialysis of the solution and the consequent formation of large concentration gradients of both protons and buffer counterions near the electrode surfaces. The modeling and simulation results showed that despite the addition of 1.0 M of buffering agent to the bulk of the solution, during operation significant pH gradients developed near the surfaces of the electrodes. Hence, although the bulk electrolyte was buffered to near-neutral pH, the electrode surfaces and electrocatalysts experienced local environments under steady-state operation that were either highly acidic or highly alkaline in nature, changing the chemical form of the electrocatalysts and exposing the electrodes to potentially corrosive local pH conditions. In addition to significant pH gradients, the STH conversion efficiency of both types of systems was limited by the mass transport of ionic species to the electrode surfaces. Even at operating current densities of <3 mA cm^(\u22122), the voltage drops due to these pH gradients exceeded the combined electrocatalyst overpotentials for the hydrogen- and oxygen-evolution reactions at current densities of 10 mA cm^(\u22122). Hence, such near-neutral pH solar-driven water-splitting systems were both fundamentally limited in efficiency and/or co-evolved explosive mixtures of H_2(g) and O_2(g) in the presence of active catalysts for the recombination of H_2(g) and O_2(g).", "doi": "10.1039/c4ee01824a", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2014-10", "series_number": "10", "volume": "7", "issue": "10", "pages": "3371-3380" }, { "id": "authors:7hsq8-3g478", "collection": "authors", "collection_id": "7hsq8-3g478", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140422-103752009", "type": "article", "title": "Comparison between the measured and modeled hydrogen-evolution activity of Ni- or Pt-coated silicon photocathodes", "author": [ { "family_name": "Huang", "given_name": "Zhuangqun", "clpid": "Huang-Zhuangqun" }, { "family_name": "McKone", "given_name": "James R.", "orcid": "0000-0001-6445-7884", "clpid": "McKone-J-R" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Grimm", "given_name": "Ronald L.", "orcid": "0000-0003-0407-937X", "clpid": "Grimm-R-L" }, { "family_name": "Warren", "given_name": "Emily L.", "orcid": "0000-0001-8568-7881", "clpid": "Warren-E-L" }, { "family_name": "Spurgeon", "given_name": "Joshua M.", "orcid": "0000-0002-2987-0865", "clpid": "Spurgeon-J-M" }, { "family_name": "Lewerenz", "given_name": "Hans-Joachim", "orcid": "0000-0001-8433-9471", "clpid": "Lewerenz-H-J" }, { "family_name": "Brunschwig", "given_name": "Bruce S.", "orcid": "0000-0002-6135-6727", "clpid": "Brunschwig-B-S" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The electrocatalytic behavior of Ni and Pt nanoparticles for the hydrogen-evolution reaction (HER) on p-type Si photocathodes was measured experimentally and the current density vs. potential (J\u2013E) characteristics of a general metal catalyst on p-Si was modeled as a combination of a Si photodiode in series electrically with metal electrocatalysts. Relative to the rest potential, the J\u2013E characteristics produced by the model showed an increase in total overpotential required to reach a specified current density for the metallized photoelectrodes relative to that of a metal electrode. This prediction was in accord with the experimentally observed behavior of Pt on p-Si, but was in contrast to the behavior observed for Ni on p-Si. Properly accounting for junction energetics and kinetics of the HER is critical to accurate predictions of the solar-to-hydrogen (STH) energy-conversion efficiency of metallized integrated photoelectrochemical systems. Further, models that accurately predict the performance of metal catalysts on semiconductor light absorbers are required to optimize the catalytic performance of metallized photoelectrodes.", "doi": "10.1016/j.ijhydene.2013.12.162", "issn": "0360-3199", "publisher": "Elsevier", "publication": "International Journal of Hydrogen Energy", "publication_date": "2014-09-23", "series_number": "28", "volume": "39", "issue": "28", "pages": "16220-16226" }, { "id": "authors:yny2z-2pb07", "collection": "authors", "collection_id": "yny2z-2pb07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141001-112924015", "type": "article", "title": "Modeling the Performance of an Integrated Photoelectrolysis System with 10\u00d7 Solar Concentrators", "author": [ { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "Two designs for an integrated photoelectrolysis system that uses a 10\u00d7 concentrating solar collector have been investigated in detail. The system performance was evaluated using a multi-physics model that accounted for the properties of the tandem photoabsorbers, mass transport, and the electrocatalytic performance of the oxygen-evolution and hydrogen-evolution reactions (OER and HER, respectively). The solar-to-hydrogen (STH) conversion efficiencies and the ohmic losses associated with proton transport in the solution electrolyte and through the membrane of the photoelectrolysis system were evaluated systematically as a function of the cell dimensions, the operating temperatures, the bandgap combinations of the tandem cell, and the performance of both the photoabsorbers and electrocatalysts. Relative to designs of optimized systems that would operate without a solar concentrator, the optimized 10\u00d7 solar concentrator designs possessed larger ohmic losses and exhibited less uniformity in the distribution of the current density along the width of the photoelectrode. To minimize resistive losses while maximizing the solar-to-hydrogen conversion efficiency, \u03b7_(STH), both of the designs, a two-dimensional \"trough\" design and a three-dimensional \"bubble wrap\" design, required that the electrode width or diameter, respectively, was no larger than a few millimeters. As the size of the electrodes increased beyond this limiting dimension, the \u03b7_(STH) became more sensitive to the performance of the photoabsorbers and catalysts. At a fixed electrode dimension, increases in the operating temperature reduced the efficiency of cells with smaller electrodes, due to degradation in the performance of the photoabsorber with increasing temperature. In contrast, cells with larger electrode dimensions showed increases in efficiency as the temperature increased, due to increases in the rates of electrocatalysis and due to enhanced mass transport. The simulations indicted that cells that contained 10% photoabsorber area, and minimal amounts of Nafion or other permselective membranes (i.e. areal coverages and volumetric fractions of only a few percent of the cell), with the remaining area comprised of a suitable, low-cost inert, non porous material (flexible polymers, inert inorganic materials, etc.) should be able to produce high values of \u03b7_(STH), with \u03b7_(STH) = 29.8% for an optimized design with a bandgap combination of 1.6 eV/0.9 eV in a tandem photoabsorber system at 350 K.", "doi": "10.1149/2.0751410jes", "issn": "0013-4651", "publisher": "Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "2014-08-01", "series_number": "10", "volume": "161", "issue": "10", "pages": "F1101-F1110" }, { "id": "authors:8t4ef-w2q72", "collection": "authors", "collection_id": "8t4ef-w2q72", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140425-070837177", "type": "article", "title": "Two stories from the ISACS 12 conference: solar-fuel devices and catalyst identification", "author": [ { "family_name": "Huang", "given_name": "Zhuangqun", "clpid": "Huang-Zhuangqun" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Lewerenz", "given_name": "Hans-Joachim", "orcid": "0000-0001-8433-9471", "clpid": "Lewerenz-H-J" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The International Symposia for\nadvancing the Chemical Sciences, a\npartner of the journal Chemical Science,\nheld its 12th meeting (ISACS 12) at the\nUniversity of Cambridge on September\n3\u20136 2013. ISACS 12 focused on \"Challenges\nin Chemical Renewable Energy\",\nwith oral presentations organized along\nfive themes: photovoltaics, solar fuels,\nmolecular and bio-inspired catalysts, new\nmaterials for batteries, and fuel cells.\nISACS 12 also included a presentation on\nthe sugar cane-based energy industry in\nBrazil, a recording by the BBC World\nService, and two poster sessions. This\nconference was an exciting, busy place to\nmeet people, exchange ideas, and foster\ncollaboration.", "doi": "10.1039/c3ee90043f", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2014-04", "series_number": "4", "volume": "7", "issue": "4", "pages": "1207-1211" }, { "id": "authors:9n51x-geg81", "collection": "authors", "collection_id": "9n51x-geg81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140731-100438286", "type": "article", "title": "High-Throughput Mapping of the Electrochemical Properties of (Ni-Fe-Co-Ce)O_x Oxygen-Evolution Catalysts", "author": [ { "family_name": "Haber", "given_name": "Joel A.", "orcid": "0000-0001-7847-5506", "clpid": "Haber-J-A" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Guevarra", "given_name": "Dan", "orcid": "0000-0002-9592-3195", "clpid": "Guevarra-D-W" }, { "family_name": "Jung", "given_name": "Suho", "orcid": "0000-0002-8119-3902", "clpid": "Jung-Suho" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "abstract": "Discovering improved electrocatalysts is critical for many technologically important processes and for the development of new clean-energy technologies. High-throughput methods for measuring fundamental electrochemical properties are demonstrated through the investigation of oxygen-evolution catalysis by using 665 oxide compositions containing nickel, iron, cobalt, and cerium. The behavior of each composition is characterized in 1.0\u2009M NaOH(aq) by using a scanning drop three-electrode cell to perform chronopotentiometry (CP) and cyclic voltammetry experiments. CP measurements at different current densities identify different composition\u2013performance trends, owing to underlying variations in fundamental electrochemical behavior. We report systematic, coincident, composition-dependent trends in the Tafel slopes and the reversible redox potentials of the catalysts. Applying high-throughput electrochemical methods provides insight into composition\u2013property\u2013performance relationships and motivates new directions for the study of catalyst mechanisms by using informatics and theory.", "doi": "10.1002/celc.201300229", "issn": "2196-0216", "publisher": "Wiley", "publication": "ChemElectroChem", "publication_date": "2014-03-11", "series_number": "3", "volume": "1", "issue": "3", "pages": "524-528" }, { "id": "authors:r2fnc-ecf12", "collection": "authors", "collection_id": "r2fnc-ecf12", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140218-144233923", "type": "article", "title": "Mapping Quantum Yield for (Fe\u2212Zn\u2212Sn\u2212Ti)O_x Photoabsorbers Using a High Throughput Photoelectrochemical Screening System", "author": [ { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Haber", "given_name": "Joel", "orcid": "0000-0001-7847-5506", "clpid": "Haber-J-A" }, { "family_name": "Marcin", "given_name": "Martin", "clpid": "Marcin-M-R" }, { "family_name": "Mitrovic", "given_name": "Slobodan", "orcid": "0000-0001-8913-8505", "clpid": "Mitrovic-S" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "abstract": "Combinatorial synthesis and screening of light absorbers are critical to material discoveries for photovoltaic and photoelectrochemical applications. One of the most effective ways to evaluate the energy-conversion properties of a semiconducting light absorber is to form an asymmetric junction and investigate the photogeneration, transport and recombination processes at the semiconductor interface. This standard photoelectrochemical measurement is readily made on a semiconductor sample with a back-side metallic contact (working electrode) and front-side solution contact. In a typical combinatorial material library, each sample shares a common back contact, requiring novel instrumentation to provide spatially resolved and thus sample-resolved measurements. We developed a multiplexing counter electrode with a thin layer assembly, in which a rectifying semiconductor/liquid junction was formed and the short-circuit photocurrent was measured under chopped illumination for each sample in a material library. The multiplexing counter electrode assembly demonstrated a photocurrent sensitivity of sub-10 \u03bcA cm^(\u20132) with an external quantum yield sensitivity of 0.5% for each semiconductor sample under a monochromatic ultraviolet illumination source. The combination of cell architecture and multiplexing allows high-throughput modes of operation, including both fast-serial and parallel measurements. To demonstrate the performance of the instrument, the external quantum yields of 1819 different compositions from a pseudoquaternary metal oxide library, (Fe\u2013Zn\u2013Sn\u2013Ti)O_x, at 385 nm were collected in scanning serial mode with a throughput of as fast as 1 s per sample. Preliminary screening results identified a promising ternary composition region centered at Fe_(0.894)Sn_(0.103)Ti_(0.0034)O_x, with an external quantum yield of 6.7% at 385 nm.", "doi": "10.1021/co400081w", "issn": "2156-8952", "publisher": "American Chemical Society", "publication": "ACS Combinatorial Science", "publication_date": "2014-03-10", "series_number": "3", "volume": "16", "issue": "3", "pages": "120-127" }, { "id": "authors:5d5kq-kdn76", "collection": "authors", "collection_id": "5d5kq-kdn76", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140127-093320786", "type": "article", "title": "High-Throughput Bubble Screening Method for Combinatorial Discovery of Electrocatalysts for Water Splitting", "author": [ { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Suram", "given_name": "Santosh K.", "orcid": "0000-0001-8170-2685", "clpid": "Suram-S-K" }, { "family_name": "Haber", "given_name": "Joel A.", "orcid": "0000-0001-7847-5506", "clpid": "Haber-J-A" }, { "family_name": "Guevarra", "given_name": "Dan W.", "orcid": "0000-0002-9592-3195", "clpid": "Guevarra-D-W" }, { "family_name": "Soedarmadji", "given_name": "Ed", "clpid": "Soedarmadji-E" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "abstract": "Combinatorial synthesis and screening for discovery of electrocatalysts has received increasing attention, particularly for energy-related technologies. High-throughput discovery strategies typically employ a fast, reliable initial screening technique that is able to identify active catalyst composition regions. Traditional electrochemical characterization via current\u2013voltage measurements is inherently throughput-limited, as such measurements are most readily performed by serial screening. Parallel screening methods can yield much higher throughput and generally require the use of an indirect measurement of catalytic activity. In a water-splitting reaction, the change of local pH or the presence of oxygen and hydrogen in the solution can be utilized for parallel screening of active electrocatalysts. Previously reported techniques for measuring these signals typically function in a narrow pH range and are not suitable for both strong acidic and basic environments. A simple approach to screen the electrocatalytic activities by imaging the oxygen and hydrogen bubbles produced by the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is reported here. A custom built electrochemical cell was employed to record the bubble evolution during the screening, where the testing materials were subject to desired electrochemical potentials. The transient of the bubble intensity obtained from the screening was quantitatively analyzed to yield a bubble figure of merit (FOM) that represents the reaction rate. Active catalysts in a pseudoternary material library, (Ni\u2013Fe\u2013Co)O_x, which contains 231 unique compositions, were identified in less than one minute using the bubble screening method. An independent, serial screening method on the same material library exhibited excellent agreement with the parallel bubble screening. This general approach is highly parallel and is independent of solution pH.", "doi": "10.1021/co400151h", "issn": "2156-8952", "publisher": "American Chemical Society", "publication": "ACS Combinatorial Science", "publication_date": "2014-02", "series_number": "2", "volume": "16", "issue": "2", "pages": "47-52" }, { "id": "authors:nk9pt-j4552", "collection": "authors", "collection_id": "nk9pt-j4552", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140325-130923791", "type": "article", "title": "Discovering Ce-rich oxygen evolution catalysts, from high throughput screening to water electrolysis", "author": [ { "family_name": "Haber", "given_name": "Joel A.", "orcid": "0000-0001-7847-5506", "clpid": "Haber-J-A" }, { "family_name": "Cai", "given_name": "Yun", "clpid": "Cai-Yun" }, { "family_name": "Jung", "given_name": "Suho", "orcid": "0000-0002-8119-3902", "clpid": "Jung-Suho" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Mitrovic", "given_name": "Slobodan", "orcid": "0000-0001-8913-8505", "clpid": "Mitrovic-S" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" }, { "family_name": "Bell", "given_name": "Alexis T.", "orcid": "0000-0002-5738-4645", "clpid": "Bell-A-T" }, { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" } ], "abstract": "We report a new Ce-rich family of active oxygen evolution reaction (OER) catalysts composed of earth abundant elements, discovered using high-throughput methods. High resolution inkjet printing was used to produce 5456 discrete oxide compositions containing the elements nickel, iron, cobalt and cerium. The catalytic performance of each of these compositions was measured under conditions applicable to distributed solar fuels generation using a three-electrode scanning drop electrochemical cell. The catalytic activity and stability of representative compositions (Ni_(0.5)Fe_(0.3)Co_(0.17)Ce_(0.03)O_x and Ni_(0.3)Fe^(0.07)Co_(0.2)Ce_(0.43)O_x) from 2 distinct regions were verified by resynthesizing these compositions on glassy carbon rods for electrochemical testing. The activity of the new Ce-rich catalysts was further verified using an unrelated synthetic method to electrodeposit a pseudo-ternary composition Ni_(0.2)Co_(0.3)Ce_(0.5)O_x, which produced a catalyst with 10 mA cm^(\u22122) oxygen evolution current at 310 mV overpotential. The unique Tafel behavior of these Ce-rich catalysts affords the opportunity for further improvement.", "doi": "10.1039/C3EE43683G", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2014-02", "series_number": "2", "volume": "7", "issue": "2", "pages": "682-688" }, { "id": "authors:7yt9f-1n253", "collection": "authors", "collection_id": "7yt9f-1n253", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140617-094404706", "type": "article", "title": "Enabling Solar Fuels Technology With High Throughput Experimentation", "author": [ { "family_name": "Gregoire", "given_name": "J. M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" }, { "family_name": "Haber", "given_name": "J. A.", "orcid": "0000-0001-7847-5506", "clpid": "Haber-J-A" }, { "family_name": "Mitrovic", "given_name": "S.", "orcid": "0000-0001-8913-8505", "clpid": "Mitrovic-S" }, { "family_name": "Xiang", "given_name": "C.", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Suram", "given_name": "S.", "orcid": "0000-0001-8170-2685", "clpid": "Suram-S-K" }, { "family_name": "Newhouse", "given_name": "P. F.", "orcid": "0000-0003-2032-3010", "clpid": "Newhouse-P-F" }, { "family_name": "Soedarmadji", "given_name": "E.", "clpid": "Soedarmadji-E" }, { "family_name": "Marcin", "given_name": "M.", "clpid": "Marcin-M" }, { "family_name": "Kan", "given_name": "K.", "clpid": "Kan-Kevin" }, { "family_name": "Guevarra", "given_name": "D.", "orcid": "0000-0002-9592-3195", "clpid": "Guevarra-D" }, { "family_name": "Jones", "given_name": "R.", "clpid": "Jones-R" }, { "family_name": "Becerra", "given_name": "N.", "clpid": "Becerra-N" }, { "family_name": "Cornell", "given_name": "E. W.", "clpid": "Cornell-E-W" }, { "family_name": "Jin", "given_name": "J.", "clpid": "Jin-Jian" } ], "abstract": "The High Throughput Experimentation (HTE) project of the Joint Center for Artificial Photosynthesis (JCAP, http://solarfuelshub.org/) performs accelerated discovery of new earth-abundant photoabsorbers and electrocatalysts. Through collaboration within the DOE solar fuels hub and with the broader research community, the new materials will be utilized in devices that efficiently convert solar energy, water and carbon dioxide into transportation fuels. JCAP-HTE builds high-throughput pipelines for the synthesis, screening and characterization of photoelectrochemical materials. In addition to a summary of these pipelines, we will describe several new screening instruments for high throughput (photo-)electrochemical measurements. These instruments are not only optimized for screening against solar fuels requirements, but also provide new tools for the broader combinatorial materials science community. We will also describe the high throughput discovery, follow-on verification, and device implementation of a new quaternary metal oxide catalyst. This rapid technology development from discovery to device implementation is a hallmark of the multi-faceted JCAP research effort.", "doi": "10.1557/opl.2014.29", "issn": "1946-4274", "publisher": "Materials Research Society", "publication": "MRS Proceedings", "publication_date": "2014-01-07", "volume": "1654", "pages": "Art. No. opl.2014.29" }, { "id": "authors:cjemv-sr524", "collection": "authors", "collection_id": "cjemv-sr524", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131223-104331588", "type": "article", "title": "Modeling an integrated photoelectrolysis system sustained by water vapor", "author": [ { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Chen", "given_name": "Yikai", "clpid": "Chen-Yikai" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "Two designs for an integrated photoelectrolysis system sustained by water vapor have been investigated using a multi-physics numerical model that accounts for charge and species conservation, electron and ion transport, and electrochemical processes. Both designs leverage the use of a proton-exchange membrane that provides conductive pathways for reactant/product transport and prevents product crossover. The resistive losses, product gas transport, and gas crossovers as a function of the geometric parameters of the two designs have been evaluated systematically. In these designs, minimization of pathways in the membrane that can support the diffusive transport of product gases from the catalyst to the gas-collecting chamber was required to prevent supersaturation of hydrogen or oxygen gases at the Nafion/catalyst interface. Due to the small, thin membrane layer that was required, a small electrode width (<300 \u03bcm) was also required to produce low resistive losses in the system. Alternatively, incorporation of a structured membrane that balances the gas transport and ionic transport allows the maximum electrode width to be increased to dimensions as large as a few millimeters. Diffusive gas transport between the cathode and anode was the dominant source for crossover of the product gases under such circumstances. The critical dimension of the electrode required to produce acceptably low rates of product crossover was also investigated through the numerical modeling and device simulations.", "doi": "10.1039/c3ee42143k", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2013-12", "series_number": "12", "volume": "6", "issue": "12", "pages": "3713-3721" }, { "id": "authors:jwtmz-ngq09", "collection": "authors", "collection_id": "jwtmz-ngq09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131224-102701042", "type": "article", "title": "Simulations of the irradiation and temperature dependence of the efficiency of tandem photoelectrochemical water-splitting systems", "author": [ { "family_name": "Haussener", "given_name": "Sophia", "orcid": "0000-0002-3044-1662", "clpid": "Haussener-S" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-A-Z" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The instantaneous efficiency of an operating photoelectrochemical solar-fuel-generator system is a complicated function of the tradeoffs between the light intensity and temperature-dependence of the photovoltage and photocurrent, as well as the losses associated with factors that include ohmic resistances, concentration overpotentials, kinetic overpotentials, and mass transport. These tradeoffs were evaluated quantitatively using an advanced photoelectrochemical device model comprised of an analytical device physics model for the semiconducting light absorbers in combination with a multi-physics device model that solved for the governing conservation equations in the various other parts of the system. The model was used to evaluate the variation in system efficiency due to hourly and seasonal variations in solar irradiation as well as due to variation in the isothermal system temperature. The system performance characteristics were also evaluated as a function of the band gaps of the dual-absorber tandem component and its properties, as well as the device dimensions and the electrolyte conductivity. The modeling indicated that the system efficiency varied significantly during the day and over a year, exhibiting local minima at midday and a global minimum at midyear when the solar irradiation is most intense. These variations can be reduced by a favorable choice of the system dimensions, by a reduction in the electrolyte ohmic resistances, and/or by utilization of very active electrocatalysts for the fuel-producing reactions. An increase in the system temperature decreased the annual average efficiency and led to less rapid ramp-up and ramp-down phases of the system, but reduced midday and midyear instantaneous efficiency variations. Careful choice of the system dimensions resulted in minimal change in the system efficiency in response to degradation in the quality of the light absorbing materials. The daily and annually averaged mass of hydrogen production for the optimized integrated system compared favorably to the daily and annually averaged mass of hydrogen that was produced by an optimized stand-alone tandem photovoltaic array connected electrically to a stand-alone electrolyzer system. The model can be used to predict the performance of the system, to optimize the design of solar-driven water splitting devices, and to guide the development of components of the devices as well as of the system as a whole.", "doi": "10.1039/c3ee41302k", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2013-12", "series_number": "12", "volume": "6", "issue": "12", "pages": "3605-3618" }, { "id": "authors:j3j2v-49s47", "collection": "authors", "collection_id": "j3j2v-49s47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131118-152050309", "type": "article", "title": "An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems", "author": [ { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Haussener", "given_name": "Sophia", "orcid": "0000-0002-3044-1662", "clpid": "Haussener-S" }, { "family_name": "Berger", "given_name": "Alan D.", "clpid": "Berger-A-D" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The solar-to-hydrogen (STH) efficiency limits, along with the maximum efficiency values and the corresponding optimal band gap combinations, have been evaluated for various combinations of light absorbers arranged in a tandem configuration in realistic, operational water-splitting prototypes. To perform the evaluation, a current\u2013voltage model was employed, with the light absorbers, electrocatalysts, solution electrolyte, and membranes coupled in series, and with the directions of optical absorption, carrier transport, electron transfer and ionic transport in parallel. The current density vs. voltage characteristics of the light absorbers were determined by detailed-balance calculations that accounted for the Shockley\u2013Queisser limit on the photovoltage of each absorber. The maximum STH efficiency for an integrated photoelectrochemical system was found to be ~31.1% at 1 Sun (=1 kW m\u207b\u00b2, air mass 1.5), fundamentally limited by a matching photocurrent density of 25.3 mA cm\u207b\u00b2 produced by the light absorbers. Choices of electrocatalysts, as well as the fill factors of the light absorbers and the Ohmic resistance of the solution electrolyte also play key roles in determining the maximum STH efficiency and the corresponding optimal tandem band gap combination. Pairing 1.6\u20131.8 eV band gap semiconductors with Si in a tandem structure produces promising light absorbers for water splitting, with theoretical STH efficiency limits of >25%.", "doi": "10.1039/c3ee40453f", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2013-10", "series_number": "10", "volume": "6", "issue": "10", "pages": "2984-2993" }, { "id": "authors:67szj-e5a08", "collection": "authors", "collection_id": "67szj-e5a08", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230329-637828000.2", "type": "article", "title": "Simulations of the Irradiation and Temperature Dependence of the Efficiency of Tandem Photoelectrochemical Water-splitting Systems", "author": [ { "family_name": "Haussener", "given_name": "Sophia", "orcid": "0000-0002-3044-1662", "clpid": "Haussener-Sophia" }, { "family_name": "Hu", "given_name": "Shu", "orcid": "0000-0002-5041-0169", "clpid": "Hu-Shu" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-Adam-Z" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The efficiency of an operating photoelectrochemical solar-fuels-generator system is determined by the system design, the properties and morphology of the system's components, and the operational conditions. We used a previously developed model comprising of i) the detailed balance limit to describe the currentpotential performance of the photoabsorber component, and ii) the detailed multi-physics device model solving for the governing conservation equations (mass, momentum, species and charge) spatially resolved in the device, to quantify the performance of photoelectrochemical devices. The investigated the performance and its variations as a function of operational conditions, i.e. daily and seasonal irradiation variations, concentration factor of irradiation, and isothermal device temperature. Additionally, the difference in performance of an integrated photoelectrochemical system and a photovoltaic array connected electrically to a standalone electrolyzer system was quantified.", "doi": "10.1149/05802.0293ecst", "issn": "1938-5862", "publisher": "Electrochemical Society", "publication": "ECS Transactions", "publication_date": "2013-08-31", "series_number": "2", "volume": "58", "issue": "2", "pages": "293-303" }, { "id": "authors:j997w-2d154", "collection": "authors", "collection_id": "j997w-2d154", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140609-083826658", "type": "article", "title": "Combined Catalysis and Optical Screening for High Throughput Discovery of Solar Fuels Catalysts", "author": [ { "family_name": "Gregoire", "given_name": "J. M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" }, { "family_name": "Xiang", "given_name": "C.", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Mitrovic", "given_name": "S.", "orcid": "0000-0001-8913-8505", "clpid": "Mitrovic-S" }, { "family_name": "Liu", "given_name": "X.", "clpid": "Liu-Xiaonao" }, { "family_name": "Marcin", "given_name": "M.", "clpid": "Marcin-M-R" }, { "family_name": "Cornell", "given_name": "E. W.", "clpid": "Cornell-E-W" }, { "family_name": "Fan", "given_name": "J.", "clpid": "Fan-J" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" } ], "abstract": "Considerable research and development efforts are being devoted to the efficient generation of solar fuels. A solar fuels device couples a solar photoabsorber with catalysts to convert solar energy to chemical energy via reactions such as oxygen evolution (water splitting). Widespread deployment of this technology hinges upon discovery of new materials through efforts such as the high throughput screening of oxygen evolution catalysts, as discussed in this manuscript. We derive an expression for the efficiency of the oxygen evolution catalyst that combines catalytic and optical properties. Using this hybrid efficiency, we screen 5456 samples in a (Fe-Co-Ni-Ti)O_x pseudo-quaternary catalyst library using automated, high throughput electrochemistry and optical experiments. The observed compositional trends in this catalyst efficiency lead to the discovery of a new high performance composition region.", "doi": "10.1149/05049.0009ecst", "issn": "1938-5862", "publisher": "Electrochemical Society", "publication": "ECS Transactions", "publication_date": "2013-06-20", "series_number": "49", "volume": "50", "issue": "49", "pages": "9-20" }, { "id": "authors:8zktp-36848", "collection": "authors", "collection_id": "8zktp-36848", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130509-154116203", "type": "article", "title": "Scanning droplet cell for high throughput electrochemical and photoelectrochemical measurements", "author": [ { "family_name": "Gregoire", "given_name": "John M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Liu", "given_name": "Xiaonao", "clpid": "Liu-Xiaonao" }, { "family_name": "Marcin", "given_name": "Martin", "clpid": "Marcin-M-R" }, { "family_name": "Jin", "given_name": "Jian", "clpid": "Jin-Jian" } ], "abstract": "High throughput electrochemical techniques are widely applied in material discovery and optimization. For many applications, the most desirable electrochemical characterization requires a three-electrode cell under potentiostat control. In high throughput screening, a material library is explored by either employing an array of such cells, or rastering a single cell over the library. To attain this latter capability with unprecedented throughput, we have developed a highly integrated, compact scanning droplet cell that is optimized for rapid electrochemical and photoeletrochemical measurements. Using this cell, we screened a quaternary oxide library as (photo)electrocatalysts for the oxygen evolution (water splitting) reaction. High quality electrochemical measurements were carried out and key electrocatalytic properties were identified for each of 5456 samples with a throughput of 4 s per sample.", "doi": "10.1063/1.4790419", "issn": "0034-6748", "publisher": "American Institute of Physics", "publication": "Review of Scientific Instruments", "publication_date": "2013-02", "series_number": "2", "volume": "84", "issue": "2", "pages": "Art. No. 024102" }, { "id": "authors:7efrp-r4852", "collection": "authors", "collection_id": "7efrp-r4852", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130523-112147351", "type": "article", "title": "Combined Catalysis and Optical Screening for High Throughput Discovery of Solar Fuels Catalysts", "author": [ { "family_name": "Gregoire", "given_name": "J. M.", "orcid": "0000-0002-2863-5265", "clpid": "Gregoire-J-M" }, { "family_name": "Xiang", "given_name": "C.", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Mitrovic", "given_name": "S.", "orcid": "0000-0001-8913-8505", "clpid": "Mitrovic-S" }, { "family_name": "Liu", "given_name": "X.", "clpid": "Liu-Xiaonao" }, { "family_name": "Marcin", "given_name": "M.", "clpid": "Marcin-M-R" }, { "family_name": "Cornell", "given_name": "E. W.", "clpid": "Cornell-E-W" }, { "family_name": "Fan", "given_name": "J.", "clpid": "Fan-J" }, { "family_name": "Jin", "given_name": "J.", "clpid": "Jin-Jian" } ], "abstract": "Considerable research and development efforts are being devoted to the efficient generation of solar fuels. A solar fuels device\ncouples a solar photoabsorber with catalysts to convert solar energy to chemical energy via reactions such as oxygen evolution\n(water splitting). Widespread deployment of this technology hinges upon discovery of new materials through efforts such as the high\nthroughput screening of oxygen evolution catalysts, as discussed in this manuscript. We derive an expression for the efficiency of\nthe oxygen evolution catalyst that combines catalytic and optical properties. Using this hybrid efficiency, we screen 5456 samples in\na (Fe-Co-Ni-Ti)O_x pseudo-quaternary catalyst library using automated, high throughput electrochemical and optical experiments.\nThe observed compositional trends in this catalyst efficiency lead to the discovery of a new high performance composition region.", "doi": "10.1149/2.035304jes", "issn": "0013-4651", "publisher": "Electrochemical Society", "publication": "Journal of the Electrochemical Society", "publication_date": "2013-01-30", "series_number": "4", "volume": "160", "issue": "4", "pages": "F337-F342" }, { "id": "authors:q367t-vbq61", "collection": "authors", "collection_id": "q367t-vbq61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130107-104614254", "type": "article", "title": "Modeling, simulation, and design criteria for photoelectrochemical water-splitting systems", "author": [ { "family_name": "Haussener", "given_name": "Sophia", "orcid": "0000-0002-3044-1662", "clpid": "Haussener-S" }, { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Spurgeon", "given_name": "Joshua M.", "orcid": "0000-0002-2987-0865", "clpid": "Spurgeon-J-M" }, { "family_name": "Ardo", "given_name": "Shane", "orcid": "0000-0001-7162-6826", "clpid": "Ardo-S" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Weber", "given_name": "Adam Z.", "orcid": "0000-0002-7749-1624", "clpid": "Weber-A-Z" } ], "abstract": "A validated multi-physics numerical model that accounts for charge and species conservation, fluid flow, and electrochemical processes has been used to analyze the performance of solar-driven photoelectrochemical water-splitting systems. The modeling has provided an in-depth analysis of conceptual designs, proof-of-concepts, feasibility investigations, and quantification of performance. The modeling has led to the formulation of design guidelines at the system and component levels, and has identified quantifiable gaps that warrant further research effort at the component level. The two characteristic generic types of photoelectrochemical systems that were analyzed utilized: (i) side-by-side photoelectrodes and (ii) back-to-back photoelectrodes. In these designs, small electrode dimensions (mm to cm range) and large electrolyte heights were required to produce small overall resistive losses in the system. Additionally, thick, non-permeable separators were required to achieve acceptably low rates of product crossover.", "doi": "10.1039/c2ee23187e", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2012-12", "series_number": "12", "volume": "5", "issue": "12", "pages": "9922-9935" }, { "id": "authors:zvrkb-fkj65", "collection": "authors", "collection_id": "zvrkb-fkj65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121101-150325621", "type": "article", "title": "Evaluation and optimization of mass transport of redox species in silicon microwire-array photoelectrodes", "author": [ { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Meng", "given_name": "Andrew C.", "clpid": "Meng-A-C" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "Physical integration of a Ag electrical contact internally into a metal/substrate/microstructured Si wire array/oxide/Ag/electrolyte photoelectrochemical solar cell has produced structures that display relatively low ohmic resistance losses, as well as highly efficient mass transport of redox species in the absence of forced convection. Even with front-side illumination, such wire-array based photoelectrochemical solar cells do not require a transparent conducting oxide top contact. In contact with a test electrolyte that contained 50 mM/5.0 mM of the cobaltocenium^(+/0) redox species in CH_3CN\u20131.0 M LiClO_4, when the counterelectrode was placed in the solution and separated from the photoelectrode, mass transport restrictions of redox species in the internal volume of the Si wire array photoelectrode produced low fill factors and limited the obtainable current densities to 17.6 mA cm^(-2) even under high illumination. In contrast, when the physically integrated internal Ag film served as the counter electrode, the redox couple species were regenerated inside the internal volume of the photoelectrode, especially in regions where depletion of the redox species due to mass transport limitations would have otherwise occurred. This behavior allowed the integrated assembly to operate as a two-terminal, stand-alone, photoelectrochemical solar cell. The current density vs. voltage behavior of the integrated photoelectrochemical solar cell produced short-circuit current densities in excess of 80 mA cm^(-2) at high light intensities, and resulted in relatively low losses due to concentration overpotentials at 1 Sun illumination. The integrated wire array-based device architecture also provides design guidance for tandem photoelectrochemical cells for solar-driven water splitting.", "doi": "10.1073/pnas.1118338109", "pmcid": "PMC3465373", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2012-09-25", "series_number": "39", "volume": "109", "issue": "39", "pages": "15622-15627" }, { "id": "authors:3prmb-dte58", "collection": "authors", "collection_id": "3prmb-dte58", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110421-100446025", "type": "article", "title": "820 mV open-circuit voltages from Cu_(2)O/CH_(3)CN junctions", "author": [ { "family_name": "Xiang", "given_name": "Chengxiang", "orcid": "0000-0002-1698-6754", "clpid": "Xiang-Chengxiang" }, { "family_name": "Kimball", "given_name": "Gregory M.", "clpid": "Kimball-G-M" }, { "family_name": "Grimm", "given_name": "Ronald L.", "orcid": "0000-0003-0407-937X", "clpid": "Grimm-R-L" }, { "family_name": "Brunschwig", "given_name": "Bruce S.", "orcid": "0000-0002-6135-6727", "clpid": "Brunschwig-B-S" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "P-Type cuprous oxide (Cu_(2)O) photoelectrodes prepared by the thermal oxidation of Cu foils exhibited open-circuit voltages in excess of 800 mV in nonaqueous regenerative photoelectrochemical cells. In contact with the decamethylcobaltocene^(+/0) (Me_(10)CoCp_(2)^(+/0)) redox couple, cuprous oxide yielded open-circuit voltage, V_(oc), values of 820 mV and short-circuit current density, J_(sc), values of 3.1 mA cm^(\u22122) under simulated air mass 1.5 illumination. The energy-conversion efficiency of 1.5% was limited by solution absorption and optical reflection losses that reduced the short-circuit photocurrent density. Spectral response measurements demonstrated that the internal quantum yield approached unity in the 400\u2013500 nm spectral range, but poor red response, attributable to bulk recombination, lowered the overall efficiency of the cell. X-Ray photoelectron spectroscopy and Auger electron spectroscopy indicated that the photoelectrodes had a high-quality cuprous oxide surface, and revealed no observable photocorrosion during operation in the nonaqueous electrolyte. The semiconductor/liquid junctions thus provide a noninvasive method to investigate the \nenergy-conversion properties of cuprous oxide without the confounding factors of deleterious surface reactions.", "doi": "10.1039/c0ee00554a", "issn": "1754-5692", "publisher": "Royal Society of Chemistry", "publication": "Energy and Environmental Science", "publication_date": "2011-04", "series_number": "4", "volume": "4", "issue": "4", "pages": "1311-1318" } ]