[
{
"id": "authors:f4xqt-mpz87",
"collection": "authors",
"collection_id": "f4xqt-mpz87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201104-150508413",
"type": "article",
"title": "Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia",
"author": [
{
"family_name": "Lim",
"given_name": "Dae-Kwang",
"clpid": "Lim-Dae-Kwang"
},
{
"family_name": "Plymill",
"given_name": "Austin B.",
"clpid": "Plymill-A-B"
},
{
"family_name": "Paik",
"given_name": "Haemin",
"clpid": "Paik-Haemin"
},
{
"family_name": "Qian",
"given_name": "Xin",
"clpid": "Qian-Xin"
},
{
"family_name": "Zecevic",
"given_name": "Strahinja",
"clpid": "Zecevic-S-K"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250\u00b0C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH\u2082PO\u2084 is used to catalyze hydrogen electrooxidation. Cells were operated at 250\u00b0C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm\u00b2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 mol H\u2082/g_(cat)h.",
"doi": "10.1016/j.joule.2020.10.006",
"issn": "2542-4351",
"publisher": "Cell Press",
"publication": "Joule",
"publication_date": "2020-11-18",
"series_number": "11",
"volume": "4",
"issue": "11",
"pages": "2338-2347"
},
{
"id": "authors:cd2mk-2ay63",
"collection": "authors",
"collection_id": "cd2mk-2ay63",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180719-110553542",
"type": "article",
"title": "Atomic layer deposition of Pt@CsH_2PO_4 for the cathodes of solid acid fuel cells",
"author": [
{
"family_name": "Lim",
"given_name": "Dae-Kwang",
"clpid": "Lim-Dae-Kwang"
},
{
"family_name": "Liu",
"given_name": "Jian",
"orcid": "0000-0001-8552-1400",
"clpid": "Liu-Jian"
},
{
"family_name": "Pandey",
"given_name": "Shobhit A.",
"clpid": "Pandey-S-A"
},
{
"family_name": "Paik",
"given_name": "Haemin",
"clpid": "Paik-Haemin"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Hupp",
"given_name": "Joseph T.",
"orcid": "0000-0003-3982-9812",
"clpid": "Hupp-J-T"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "Atomic layer deposition (ALD) has been used to apply continuous Pt films on powders of the solid acid CsH_2PO_4 (CDP), in turn, used in the preparation of cathodes in solid acid fuel cells (SAFCs). The film deposition was carried out at 150\u202f\u00b0C using trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe_3) as the Pt source and ozone as the reactant for ligand removal. Chemical analysis showed a Pt growth rate of 0.09\u202f\u00b1\u202f0.01\u202fwt%/cycle subsequent to an initial nucleation delay of 84\u202f\u00b1\u202f20 cycles. Electron microscopy revealed the contiguous nature of the films prepared using 200 or more cycles. The cathode overpotential (0.48\u202f\u00b1\u202f0.02\u202fV\u202fat a current density of 200\u202fmA/cm^2) was independent of Pt deposition amount beyond the minimum required to achieve these continuous films. The cell electrochemical characteristics were moreover extremely stable with time, with the cathode overpotentials increasing by no more than 10\u202fmV over a 100\u202fh period of measurement. Thus, ALD holds promise as an effective tool in the preparation of SAFC cathodes with high activity and excellent stability.",
"doi": "10.1016/j.electacta.2018.07.076",
"issn": "0013-4686",
"publisher": "Elsevier",
"publication": "Electrochimica Acta",
"publication_date": "2018-10-20",
"volume": "288",
"pages": "12-19"
},
{
"id": "authors:9rqvm-hdw97",
"collection": "authors",
"collection_id": "9rqvm-hdw97",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110421-100326234",
"type": "article",
"title": "Advanced Electrodes for Solid Acid Fuel Cells by Platinum Deposition on CsH_(2)PO_4",
"author": [
{
"family_name": "Papandrew",
"given_name": "Alexander B.",
"clpid": "Papandrew-A-B"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Elgammal",
"given_name": "Ramez A.",
"clpid": "Elgammal-R-A"
},
{
"family_name": "\u00d6zer",
"given_name": "Mustafa M.",
"clpid": "\u00d6zer-M-M"
},
{
"family_name": "Zecevic",
"given_name": "Strahinja K.",
"clpid": "Zecevic-S-K"
}
],
"abstract": "We demonstrate cathodes for solid acid fuel cells fabricated by vapor deposition of platinum from the metalorganic precursor Pt(acac)_2 on the solid acid \nCsH_(2)PO_4 at 210 \u00b0C. A network of platinum nanoparticles with diameters of 2\u22124 nm serves as both the oxygen reduction catalyst and the electronic conductor in the electrode. Electrodes with a platinum content of 1.75 mg/cm^2 are more active for oxygen reduction than previously reported electrodes with a platinum content of 7.5 mg/cm^2. Electrodes containing <1.75 mg/cm^2 of platinum show significantly reduced catalytic activity and increased ohmic resistance indicative of a highly discontinuous catalytic-electronic platinum network.",
"doi": "10.1021/cm101147y",
"issn": "0897-4756",
"publisher": "American Chemical Society",
"publication": "Chemistry of Materials",
"publication_date": "2011-04-12",
"series_number": "7",
"volume": "23",
"issue": "7",
"pages": "1659-1667"
},
{
"id": "authors:xxs08-f0s44",
"collection": "authors",
"collection_id": "xxs08-f0s44",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100304-142450954",
"type": "article",
"title": "Engineering the Next Generation of Solid State Proton Conductors: Synthesis and Properties of Ba_(3\u2212x)K_(x)H_(x)(PO_4)_2",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Toberer",
"given_name": "Eric S.",
"clpid": "Toberer-E-S"
},
{
"family_name": "Louie",
"given_name": "Mary W.",
"clpid": "Louie-M-W"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "A new series of compounds with general chemical formula Ba_(3\u2212x)K_(x)H_(x)(PO_4)_2 has been successfully prepared. This particular stoichiometry was targeted as a candidate solid-state proton conductor because of its anticipated structural similarity to known M_(3)H(XO_4)_2 superprotonic conductors (M = Cs, Rb, NH4, K; X = Se, S) and to the known trigonal compound Ba_(3)(PO_4)_2. The materials were synthesized from aqueous solution using barium acetate, dipotassium hydrogen phosphate, and potassium hydroxide as starting materials. Through variations in the initial solution stoichiometry or the synthesis temperature, the final stoichiometry could be controlled from x ~ 0.5 to ~1. X-ray powder diffraction, energy dispersive spectroscopy chemical analysis, ^(1)H magic angle spinning (MAS) nuclear magnetic spectroscopy, and thermogravimetric analysis were all employed to establish potassium and proton incorporation. The diffraction data confirmed crystallization of a trigonal phase, and chemical analysis showed the (Ba+K):P ratio to be 3:2, consistent with the target stoichiometry. The conductivity of the Ba_(3\u2212x)K_(x)H_(x)(PO_4)_2 materials, as measured by A.C. impedance spectroscopy, is about 3 orders of magnitude greater than the end-member Ba_(3)(PO_4)_2 material with only a slight dependence on x, however, it is substantially lower than that of typical superprotonic conductors and of the M_(3)H(XO_4)_2 materials in particular. The close proximity of Ba to the hydrogen bond site is proposed to explain this behavior. At 250 \u00b0C, the conductivity is 2.4 \u00d7 10^(\u22125) S/cm for the composition x = 0.80, which, when combined with the water insolubility and the relatively high thermal stability, may render Ba_(3\u2212x)K_(x)H_(x)(PO_4)_2 an attractive alternative in selected electrochemical applications to known superprotonic conductors.",
"doi": "10.1021/cm9026539",
"issn": "0897-4756",
"publisher": "American Chemical Society",
"publication": "Chemistry of Materials",
"publication_date": "2010-02-09",
"series_number": "3",
"volume": "22",
"issue": "3",
"pages": "1186-1194"
},
{
"id": "authors:6bb6m-7ny12",
"collection": "authors",
"collection_id": "6bb6m-7ny12",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131113-161625630",
"type": "article",
"title": "From Laboratory Breakthrough to Technological Realization: The Development Path for Solid Acid Fuel Cells",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Papandrew",
"given_name": "Alex B.",
"clpid": "Papandrew-A-B"
},
{
"family_name": "Zecevic",
"given_name": "Strahinja K.",
"clpid": "Zecevic-S-K"
},
{
"family_name": "Cha",
"given_name": "SukYal",
"clpid": "Cha-SukYal"
},
{
"family_name": "Sasaki",
"given_name": "Kenji A.",
"clpid": "Sasaki-Kenji-A"
},
{
"family_name": "Varga",
"given_name": "\u00c1ron",
"clpid": "Varga-\u00c1"
},
{
"family_name": "Giapis",
"given_name": "Konstantinos P.",
"orcid": "0000-0002-7393-298X",
"clpid": "Giapis-K-P"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "[No abstract]",
"issn": "1064-8208",
"publisher": "Electrochemical Society",
"publication": "Interface",
"publication_date": "2009",
"series_number": "3",
"volume": "18",
"issue": "3",
"pages": "53-59"
},
{
"id": "authors:nty5h-2fj26",
"collection": "authors",
"collection_id": "nty5h-2fj26",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-162531297",
"type": "article",
"title": "Entropy Evaluation of the Superprotonic Phase of CsHSO_4: Pauling's Ice Rules Adjusted for Systems Containing Disordered Hydrogen-Bonded Tetrahedra",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "The entropy of the superprotonic transition (phase II \u2192 phase I) of CsHSO\u2084 is evaluated both experimentally and theoretically. Calorimetric measurements reveal a value of 14.75(22) J mol\u207b\u00b9 K\u207b\u00b9. Under the assumption that the entropy is entirely configurational, arising from both sulfate group orientational disorder and disorder in the hydrogen-bond network, we evaluated several structural models of CsHSO\u2084 for their consistency with the measured entropy. For a structure in which hydrogen-bond disorder is independent of sulfate-group orientational disorder, simple methods of calculating the number of structural configurations are inadequate. Thus, the configurational entropy of the superprotonic, disordered phase of CsHSO\u2084 is evaluated using an approach similar to that employed by Pauling to describe the residual entropy of ice at 0 K. Analogous to ice and the so-called ice rules, superprotonic CsHSO\u2084 is assumed to obey a set of structural rules. Key among these are that there is only one proton per sulfate tetrahedron and only one proton per hydrogen bond. Defects are argued to make a negligible contribution to the transition entropy. The transition entropy obtained from this model, 14.9 J mol\u207b\u00b9 K\u207b\u00b9, is in excellent agreement with the measured value. Such a match between theoretical and experimental values suggests that of all published Phase I structures, the structure proposed by Jirak\u00b2 more correctly describes the arrangements of the sulfate tetrahedra and protons attached to them. The assumption of a low defect concentration implies that the jump in proton conductivity at the transition is due to an increase in the mobility of charge carriers rather than their concentration.",
"doi": "10.1021/cm062070w",
"issn": "0897-4756",
"publisher": "American Chemical Society",
"publication": "Chemistry of Materials",
"publication_date": "2007-12-24",
"series_number": "2",
"volume": "19",
"issue": "2",
"pages": "270-279"
},
{
"id": "authors:nr5rk-07p47",
"collection": "authors",
"collection_id": "nr5rk-07p47",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131114-153427497",
"type": "article",
"title": "Local structure of interstitial Zn in \u03b2-Zn_4Sb_3",
"author": [
{
"family_name": "Toberer",
"given_name": "E. S.",
"clpid": "Toberer-E-S"
},
{
"family_name": "Sasaki",
"given_name": "K. A.",
"clpid": "Sasaki-K-A"
},
{
"family_name": "Chisholm",
"given_name": "C. R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "S. M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
},
{
"family_name": "Goddard",
"given_name": "W. A., III",
"orcid": "0000-0003-0097-5716",
"clpid": "Goddard-W-A-III"
},
{
"family_name": "Snyder",
"given_name": "G. J.",
"orcid": "0000-0003-1414-8682",
"clpid": "Snyder-G-J"
}
],
"abstract": "The low thermal conductivity of the thermoelectric material \u03b2-Zn_4Sb_3 has been linked to disorder arising from multiple interstitial Zn sites. Here we investigate the energetics and local distortions associated with these interstitial sites via DFT calculations. Our results show the \u03b2-Zn_4Sb_3 structure is able to distort into many inequivalent geometries of similar energies, suggesting a topology rich with transport pathways through energetically accessible metastable states. The occurrence of such a shallow energy landscape may explain the recently discovered liquid-like diffusivity of Zn in \u03b2-Zn_4Sb_3 \u2013 comparable to that found in superionic conductors.",
"doi": "10.1002/pssr.200701168",
"issn": "1862-6254",
"publisher": "Wiley",
"publication": "Physica Status Solidi - Rapid Research Letters",
"publication_date": "2007-11",
"series_number": "6",
"volume": "1",
"issue": "6",
"pages": "253-255"
},
{
"id": "authors:6qp53-83g83",
"collection": "authors",
"collection_id": "6qp53-83g83",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:HAIfd07",
"type": "article",
"title": "Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes",
"author": [
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Sasaki",
"given_name": "Kenji",
"clpid": "Sasaki-Kenji-A"
},
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Uda",
"given_name": "Tetsuya",
"clpid": "Uda-Tetsuya"
}
],
"abstract": "The compound CsH2PO4 has emerged as a viable electrolyte for intermediate temperature (200\u2013300 \u00b0C) fuel cells. In order to settle the question of the high temperature behavior of this material, conductivity measurements were performed by two-point AC impedance spectroscopy under humidified conditions (p[H2O] = 0.4 atm). A transition to a stable, high conductivity phase was observed at 230 \u00b0C, with the conductivity rising to a value of 2.2 \u00d7 10^\u20132 S cm^\u20131 at 240 \u00b0C and the activation energy of proton transport dropping to 0.42 eV. In the absence of active humidification, dehydration of CsH2PO4 does indeed occur, but, in contradiction to some suggestions in the literature, the dehydration process is not responsible for the high conductivity at this temperature. Electrochemical characterization by galvanostatic current interrupt (GCI) methods and three-point AC impedance spectroscopy (under uniform, humidified gases) of CsH2PO4 based fuel cells, in which a composite mixture of the electrolyte, Pt supported on carbon, Pt black and carbon black served as the electrodes, showed that the overpotential for hydrogen electrooxidation was virtually immeasurable. The overpotential for oxygen electroreduction, however, was found to be on the order of 100 mV at 100 mA cm^\u20132. Thus, for fuel cells in which the supported electrolyte membrane was only 25 \u00b5m in thickness and in which a peak power density of 415 mW cm^\u20132 was achieved, the majority of the overpotential was found to be due to the slow rate of oxygen electrocatalysis. While the much faster kinetics at the anode over those at the cathode are not surprising, the result indicates that enhancing power output beyond the present levels will require improving cathode properties rather than further lowering the electrolyte thickness. In addition to the characterization of the transport and electrochemical properties of CsH2PO4, a discussion of the entropy of the superprotonic transition and the implications for proton transport is presented.",
"doi": "10.1039/b604311a",
"issn": "1359-6640",
"publisher": "Royal Society of Chemistry",
"publication": "Faraday Discussions",
"publication_date": "2007",
"volume": "134",
"pages": "17-39"
},
{
"id": "authors:yeyrc-5hp15",
"collection": "authors",
"collection_id": "yeyrc-5hp15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:UDAessl06",
"type": "article",
"title": "Alcohol Fuel Cells at Optimal Temperatures",
"author": [
{
"family_name": "Uda",
"given_name": "Tetsuya",
"clpid": "Uda-Tetsuya"
},
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "High-power-density alcohol fuel cells can relieve many of the daunting challenges facing a hydrogen energy economy. Here, such fuel cells are achieved using CsH2PO4 as the electrolyte and integrating into the anode chamber a Cu-ZnO/Al2O3 methanol steam-reforming catalyst. The temperature of operation, ~250\u00b0C, is matched both to the optimal value for fuel cell power output and for reforming. Peak power densities using methanol and ethanol were 226 and 100 mW/cm^2, respectively. The high power output (305 mW/cm^2) obtained from reformate fuel containing 1% CO demonstrates the potential of this approach with optimized reforming catalysts and also the tolerance to CO poisoning at these elevated temperatures.",
"doi": "10.1149/1.2188069",
"issn": "1099-0062",
"publisher": "Electrochemical Society",
"publication": "Electrochemical and Solid-State Letters",
"publication_date": "2006-06",
"series_number": "6",
"volume": "9",
"issue": "6",
"pages": "A261-A264"
},
{
"id": "authors:d18eq-c4d69",
"collection": "authors",
"collection_id": "d18eq-c4d69",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CHIprb05",
"type": "article",
"title": "Superprotonic phase transition of CsHSO4: A molecular dynamics simulation study",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Jang",
"given_name": "Yun Hee",
"orcid": "0000-0002-6604-5813",
"clpid": "Jang-Yun-Hee"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
},
{
"family_name": "Goddard",
"given_name": "William A., III",
"orcid": "0000-0003-0097-5716",
"clpid": "Goddard-W-A-III"
}
],
"abstract": "The superprotonic phase transition (phase II --> phase I; 414 K) of cesium hydrogen sulfate, CsHSO4, was simulated using molecular dynamics with the \"first principles\" MSXX force field (FF). The structure, binding energy, and vibrational frequencies of the CsHSO4 monomer, the binding energy of the (H2SO4)2 dimer, and the torsion barrier of the HSO4- ion were determined from quantum mechanical calculations, and the parameters of the Dreiding FF for Cs, S, O, and H adjusted to reproduce these quantities. Each hydrogen atom was treated as bonded exclusively to a single oxygen atom (proton donor), but allowed to form hydrogen bonds to various second nearest oxygen atoms (proton acceptors). Fixed temperature-pressure (NPT) dynamics were employed to study the structure as a function of temperature from 298 to 723 K. In addition, the influence of several force field parameters, including the hydrogen torsional barrier height, hydrogen bond strength, and oxygen charge distribution, on the structural behavior of CsHSO4 was probed. Although the FF does not allow proton migration (i.e., proton jumps) between oxygen atoms, a clear phase transition occurred as demonstrated by a discrete change of unit cell symmetry (monoclinic to tetragonal), cell volume, and molar enthalpy. The dynamics of the HSO4- group reorientational motion also changed dramatically at the transition. The observation of a transition to the expected tetragonal phase using a FF in which protons cannot migrate indicates that proton diffusion does not drive the transition to the superprotonic phase. Rather, high conductivity is a consequence of the rapid reorientations that occur in the high temperature phase. Furthermore, because no input from the superprotonic phase was employed in these simulations, it may be possible to employ MD to hypothesize superprotonic materials.",
"doi": "10.1103/PhysRevB.72.134103",
"issn": "1098-0121",
"publisher": "American Physical Society",
"publication": "Physical Review B",
"publication_date": "2005-10",
"series_number": "13",
"volume": "72",
"issue": "13",
"pages": "Art. No. 134103"
},
{
"id": "authors:3aw6y-ggt76",
"collection": "authors",
"collection_id": "3aw6y-ggt76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131114-144131460",
"type": "article",
"title": "High performance solid acid fuel cells through humidity stabilization",
"author": [
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Uda",
"given_name": "Tetsuya",
"clpid": "Uda-Tetsuya"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "Although they hold the promise of clean energy, state-of-the-art fuel cells based on polymer electrolyte membrane fuel cells are inoperable above 100\u00b0C, require cumbersome humidification systems, and suffer from fuel permeation. These difficulties all arise from the hydrated nature of the electrolyte. In contrast, \"solid acids\" exhibit anhydrous proton transport and high-temperature stability. We demonstrate continuous, stable power generation for both H_2/O_2 and direct methanol fuel cells operated at \u223c250\u00b0C using a humidity-stabilized solid acid CsH_2PO_4 electrolyte.",
"doi": "10.1126/science.1090920",
"issn": "0036-8075",
"publisher": "American Association for the Advancement of Science",
"publication": "Science",
"publication_date": "2004-01-02",
"series_number": "5654",
"volume": "303",
"issue": "5654",
"pages": "68-70"
},
{
"id": "authors:ttx4q-8b963",
"collection": "authors",
"collection_id": "ttx4q-8b963",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160614-134020923",
"type": "article",
"title": "Instability of Sulfate and Selenate Solid Acids in Fuel Cell Environments",
"author": [
{
"family_name": "Merle",
"given_name": "Ryan B.",
"clpid": "Merle-R-B"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "The chemical and thermal stability of several solid acid compounds under fuel cell operating conditions has been investigated, primarily by thermogravimetric methods. Thermal decomposition of CsHSO_4, a material which has shown promise as an alternative electrolyte for proton exchange membrane (PEM) fuel cells, initiates at \u223c175\u00b0C under inert conditions. The overall decomposition process can be expressed as 2CsHSO_4 \u2192 Cs_2SO_4 + H_2O + SO_3 with Cs_2S_2O_7 appearing as an intermediate byproduct at slow heating rates. Under reducing conditions, chemical decomposition can occur via reaction with hydrogen according to 2CsHSO_4 + 4H_2 \u2192 Cs_2SO_4 + 4H_2O + H_2S. In the absence of fuel cell catalysts, this reduction reaction is slow; however, materials such as Pt, Pd, and WC are highly effective in catalyzing the reduction of sulfur and the generation of H_2S. In the case of M_3H(XO_4)_2 compounds, where M = Cs, NH_4, or Rb and X = S or Se, a similar reduction reaction occurs:\u2009 2M_3H(XO_4)_2 + 4H_2 \u2192 3M_2XO_4 + 4H_2O + H_2X. In an operational fuel cell based on CsHSO_4, performance degraded with time, presumably as a result of H_2S poisoning of the anode catalyst. The performance loss was recoverable by exposure of the fuel cell to air at 160 \u00b0C.",
"doi": "10.1021/ef0201174",
"issn": "1520-5029",
"publisher": "American Chemical Society",
"publication": "Energy and Fuels",
"publication_date": "2003-01",
"series_number": "1",
"volume": "17",
"issue": "1",
"pages": "210-215"
},
{
"id": "authors:g1yv2-8m120",
"collection": "authors",
"collection_id": "g1yv2-8m120",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-162531441",
"type": "article",
"title": "Superprotonic Phase Transition in CsH(PO_3H)",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Merle",
"given_name": "Ryan B.",
"clpid": "Merle-R-B"
},
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "High-temperature investigations of the compound CsH(PO\u2083H) (or CsH\u2082PO\u2083, cesium hydrogen phosphite) revealed that this material undergoes a transition, with an onset of 137 \u00b0C, to a phase of high proton conductivity. The transition is accompanied by a large heat of transformation, \u0394H = 58 \u00b1 2 J/g (12.4 \u00b1 0.4 kJ/mol), and exhibits measurable hysteresis, occurring at 96 \u00b0C upon cooling. High-temperature X-ray powder diffraction showed that the high-temperature phase is cubic, with a\u2080 = 4.896(1)\u00c5, and likely takes on a CsCl structure, with Cs atoms at the corners of a simple cubic unit cell, and PO\u2083H groups at the center. The conductivity in the high-temperature phase at 160 \u00b0C is 5.5 \u00d7 10\u207b\u00b3 \u03a9\u207b\u00b9 cm\u207b\u00b9, and the activation energy for proton transport is 0.40 \u00b1 0.01 eV. These values suggest that proton transport is facilitated by rapid PO\u2083H group reorientations in the cubic phase of CsH(PO\u2083H), as is known to occur in the high-temperature, tetragonal phase of CsHSO\u2084.",
"doi": "10.1021/cm020297v",
"issn": "0897-4756",
"publisher": "American Chemical Society",
"publication": "Chemistry of Materials",
"publication_date": "2002-08-23",
"series_number": "9",
"volume": "14",
"issue": "9",
"pages": "3889-3893"
},
{
"id": "authors:w85rw-r5076",
"collection": "authors",
"collection_id": "w85rw-r5076",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-162530597",
"type": "article",
"title": "Synthesis, Structure, and Properties of Compounds in the NaHSO_4\u2212CsHSO_4 System. 2. The Absence of Superprotonic Transitions in Cs_2Na(HSO_4)_3 and CsNa_2(HSO_4_)3",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Cowan",
"given_name": "Lisa A.",
"clpid": "Cowan-L-A"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "Exploratory synthesis in the NaHSO\u2084\u2212CsHSO\u2084 system, aimed at discovering novel proton-conducting solids, yielded the new compounds CsNa\u2082(HSO\u2084)\u2083 and Cs\u2082Na(HSO\u2084)\u2083. Thermal analysis demonstrated the absence of phase transitions for both compounds prior to melting. The conductivities of the two compounds vary monotonically with temperature, in a non-Arrhenius manner, from ambient to the respective melt temperatures of 398 and 413 K. At 363 K the conductivities are on the order of 10\u207b\u2078 \u03a9\u00b9\u207bcm\u207b\u00b9, which is comparable to that of other alkali acid sulfates. The absence of transitions to disordered, high conductivity phases, as is observed in compounds such as CsHSO\u2084, is explained in terms of the stiffness of the Na\u2212O bonds, which may serve to prevent rapid reorientation of SO\u2084 tetrahedral groups.",
"doi": "10.1021/cm0101430",
"issn": "0897-4756",
"publisher": "American Chemical Society",
"publication": "Chemistry of Materials",
"publication_date": "2001-08-21",
"series_number": "9",
"volume": "13",
"issue": "9",
"pages": "2909-2912"
},
{
"id": "authors:3wg8y-zan33",
"collection": "authors",
"collection_id": "3wg8y-zan33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-162530731",
"type": "article",
"title": "Synthesis, Structure, and Properties of Compounds in the NaHSO_4\u2212CsHSO_4 System. 1. Crystal Structures of Cs_2Na(HSO_4)_3 and CsNa_2(HSO_4_)3",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Cowan",
"given_name": "Lisa A.",
"clpid": "Cowan-L-A"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
},
{
"family_name": "Klooster",
"given_name": "Wim T.",
"clpid": "Klooster-W-T"
}
],
"abstract": "Exploratory synthesis in the NaHSO\u2084-CsHSO\u2084 system, aimed at discovering novel proton conducting solids, resulted in the new compounds CsNa\u2082(HSO\u2084)\u2083 and Cs\u2082Na(HSO\u2084)\u2083. Single-crystal X-ray diffraction (performed at room temperature) revealed CsNa\u2082(HSO\u2084)\u2083 to crystallize in the cubic space group P2\u20813 with lattice parameters a=10.568(2)\u00c5 and Z=4, whereas CS2Na(HSO\u2084)\u2083, studied by both single-crystal neutron and X-ray methods, crystallizes in the hexagonal space group P6\u2083/m. The latter compound has lattice parameters a=8.5712(17) and c=9.980(2)\u00c5, and Z=2. The unit cell volumes are 1180.4(4) and 634.9(2)\u0173, respectively, giving calculated densities of 2.645 and 3.304 mg m\u207b\u00b3. Refinement using all observed reflections yielded a weighted residual, R-w(F\u00b2), of 0.0515 based on F\u00b2 X-ray values for CsNa\u2082(HSO\u2084)\u2083. For Cs\u2082Na(HSO\u2084)\u2083 the analogous X-ray and neutron values were 0.0483 and 0.1715, respectively. Both structures contain a single, crystallographically distinct, asymmetric hydrogen bond (as confirmed by NMR investigations) and unique, three-membered (HSO\u2084)\u2083 rings. The geometric match between the NaO\u2086 octahedra and the rings suggests the sodium polyhedra may serve to template the (HSO\u2084)\u2083 unit. In CsNa\u2082(HSO\u2084)\u2083 the rings form a distorted cubic close-packed array. The Cs atoms are located within the \"octahedral\" sites of this array, and the Na atoms, within the \"tetrahedral\" sites. The rings in CS\u2082Na(HSO\u2084)\u2083 are linked together by NaO6 octahedra to form infinite Na(HSO\u2084)\u2083 chains that extend along 001. The hexagonal compound exhibits disorder about the sulfate tetrahedron that suggests a P6\u2083/m \u2192 P6 phase transition may occur upon cooling.",
"doi": "10.1021/cm000976a",
"issn": "0897-4756",
"publisher": "American Chemical Society",
"publication": "Chemistry of Materials",
"publication_date": "2001-07-17",
"series_number": "8",
"volume": "13",
"issue": "8",
"pages": "2574-2583"
},
{
"id": "authors:7zv0d-9xc54",
"collection": "authors",
"collection_id": "7zv0d-9xc54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090511-140556929",
"type": "article",
"title": "Solid acids as fuel cell electrolytes",
"author": [
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
},
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Merle",
"given_name": "Ryan B.",
"clpid": "Merle-R-B"
}
],
"abstract": "Fuel cells are attractive alternatives to combustion engines for electrical power generation because of their very high efficiencies and low pollution levels. Polymer electrolyte membrane fuel cells are generally considered to be the most viable approach for mobile applications. However, these membranes require humid operating conditions, which limit the temperature of operation to less than 100\u00b0C; they are also permeable to methanol and hydrogen, which lowers fuel efficiency. Solid, inorganic, acid compounds (or simply, solid acids) such as CsHSO_4 and Rb_3H(SeO_4)_2 have been widely studied because of their high proton conductivities and phase-transition behaviour. For fuel-cell applications they offer the advantages of anhydrous proton transport and high-temperature stability (up to 250\u00b0C). Until now, however, solid acids have not been considered viable fuel-cell electrolyte alternatives owing to their solubility in water and extreme ductility at raised temperatures (above approximately 125\u00b0C). Here we show that a cell made of a CsHSO_4 electrolyte membrane (about 1.5 mm thick) operating at 150\u2013160\u00b0C in a H_2/O_2 configuration exhibits promising electrochemical performances: open circuit voltages of 1.11 V and current densities of 44 mA cm^-2 at short circuit. Moreover, the solid-acid properties were not affected by exposure to humid atmospheres. Although these initial results show promise for applications, the use of solid acids in fuel cells will require the development of fabrication techniques to reduce electrolyte thickness, and an assessment of possible sulphur reduction following prolonged exposure to hydrogen.",
"doi": "10.1038/35073536",
"issn": "0028-0836",
"publisher": "Nature Publishing Group",
"publication": "Nature",
"publication_date": "2001-04-19",
"series_number": "6831",
"volume": "410",
"issue": "6831",
"pages": "910-913"
},
{
"id": "authors:xwarj-15y91",
"collection": "authors",
"collection_id": "xwarj-15y91",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BOYjes00",
"type": "article",
"title": "Polymer solid acid composite membranes for fuel-cell applications",
"author": [
{
"family_name": "Boysen",
"given_name": "Dane A.",
"clpid": "Boysen-D-A"
},
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
},
{
"family_name": "Narayanan",
"given_name": "Sekharipuram R.",
"clpid": "Narayanan-S-R"
}
],
"abstract": "A systematic study of the conductivity of polyvinylidene fluoride (PVDF) and CsHSO4 composites, containing 0 to 100% CsHSO4, has been carried out. The polymer, with its good mechanical properties, served as a supporting matrix for the high proton conductivity inorganic phase. The conductivity of composites exhibited a sharp increase with temperature at 142\u00b0C, characteristic of the superprotonic phase transition of CsHSO4. At high temperature (160\u00b0C), the dependence of conductivity on vol % CsHSO4 was monotonic and revealed a percolation threshold of ~10 vol %. At low temperature (100\u00b0C), a maximum in the conductivity at ~80 vol % CsHSO4 was observed. Results of preliminary fuel cell measurements are presented.",
"doi": "10.1149/1.1393947",
"issn": "0013-4651",
"publisher": "Electrochemical Society",
"publication": "Journal of the Electrochemical Society",
"publication_date": "2000-12",
"series_number": "10",
"volume": "147",
"issue": "10",
"pages": "3610-3613"
},
{
"id": "authors:f79td-e0e12",
"collection": "authors",
"collection_id": "f79td-e0e12",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-162531086",
"type": "article",
"title": "Superprotonic behavior of Cs_2(HSO_4)(H_2PO_4) \u2013 a new solid acid in the CsHSO_4\u2013CsH_2PO_4 system",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "Investigations into the CsHSO\u2084\u2013CsH\u2082PO\u2084 system have yielded a new solid acid, Cs\u2082(HSO\u2084)(H\u2082PO\u2084), with a superprotonic phase transition that occurs over the temperature range 61\u2013105\u00b0C. In the room temperature structure, the SO\u2084 and PO\u2084 groups are randomly arranged on a single tetrahedral anion site. Hydrogen bonds are distributed through the structure so as to generate a two-dimensional network quite different from that of other cesium sulfate phosphate solid acids. The transition in Cs\u2082(HSO\u2084)(H\u2082PO\u2084) takes place by a unique two-step process, occurs at an unusually low temperature, is accompanied by a large heat of transformation, \u0394H=44\u00b12 J/g, and exhibits significant hysteresis. High temperature X-ray powder diffraction (XRD) and infrared (IR) spectroscopy revealed that the high temperature phase is cubic, with a\u2080=4.926(5)\u00c5, and likely takes on a CsCl structure, with Cs atoms at the corners of a simple cubic unit cell, and XO\u2084 groups (X=P or S) at the center. The conductivity in the high temperature phase at 110\u00b0C is 3\u00d710\u207b\u00b3 \u03a9\u207b\u00b9 cm\u207b\u00b9, and the activation energy for proton transport is 0.37(1) eV. These values suggest that proton transport is facilitated by rapid XO\u2084 group reorientations in the cubic phase of Cs\u2082(HSO\u2084)(H\u2082PO\u2084), as is known to occur in the high temperature, tetragonal phase of CsHSO\u2084.",
"doi": "10.1016/S0167-2738(00)00315-5",
"issn": "0167-2738",
"publisher": "Elsevier",
"publication": "Solid State Ionics",
"publication_date": "2000-11-02",
"volume": "136",
"pages": "229-241"
},
{
"id": "authors:nqstk-69s27",
"collection": "authors",
"collection_id": "nqstk-69s27",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-162531192",
"type": "article",
"title": "X-ray structure refinement of CsHSO_4 in phase II",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "An accurate room temperature structure refinement of CsHSO_4 in phase II, the thermodynamically stable phase at temperatures below 414 K, is reported. The compound is monoclinic, space group P2_1/c, with lattice parameters a = 7.781(2), b = 8.147(2), c = 7.722(2) \u00c5, and \u03b2 = 110.78(1) \u00b0, as determined by single crystal X-ray diffraction. There are four formula units per unit cell and seven atoms in the asymmetric unit. The compound, comprised of zigzag chains of SO_4 groups alternating with zigzag rows of Cs atoms, is isostructural to CsDSO_4 A.V. Belushkin, W.I.F. David, R.M. Ibberson, L.A. Shuvalov, Acta Crystallogr. B 47 (1991) 161-166. The single, crystallographically distinct proton forms a \"symmetry-free\" hydrogen bond between O(1) and O(2). The S-O bond lengths are consistent with the presence of this bond. The hydrogen bond geometries in the protonated and deuterated compounds are within experimental error of one another, after taking due account of the difference in proton (or deuterium atom) positions as measured by X-ray and neutron diffraction.",
"doi": "10.1016/S0025-5408(00)00301-9",
"issn": "0025-5408",
"publisher": "Elsevier",
"publication": "Materials Research Bulletin",
"publication_date": "2000-05",
"series_number": "7",
"volume": "35",
"issue": "7",
"pages": "999-1005"
},
{
"id": "authors:afg0e-ksf92",
"collection": "authors",
"collection_id": "afg0e-ksf92",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131125-162530979",
"type": "article",
"title": "Structure and thermal behavior of the new superprotonic conductor Cs_2(HSO_4)(H_2PO_4)",
"author": [
{
"family_name": "Chisholm",
"given_name": "Calum R. I.",
"clpid": "Chisholm-C-R-I"
},
{
"family_name": "Haile",
"given_name": "Sossina M.",
"orcid": "0000-0002-5293-6252",
"clpid": "Haile-S-M"
}
],
"abstract": "Ongoing studies of the CsHSO_4-CsH_2PO_4 system, aimed at developing novel proton conducting solids, resulted in the new compound Cs_2(HSO_4)(H_2PO_4) (dicesium hydrogensulfate dihydrogenphosphate). Single-crystal X-ray diffraction (performed at room temperature) revealed Cs_2(HSO_4)(H_2PO_4) to crystallize in space group P2_1/n with lattice parameters a = 7.856 (8), b = 7.732 (7), c = 7.827 (7) \u00c5, and \u03b2 = 99.92 (4)\u00b0. The compound has a unit-cell volume of 468.3 (8) \u00c53 and two formula units per cell, giving a calculated density of 3.261 Mg m^(-3). Six non-H atoms and two H atoms were located in the asymmetric unit, with SO_4 and PO_4 groups randomly arranged on the single tetrahedral anion site. Refinement using all observed reflections yielded weighted residuals of 0.0890 and 0.0399 based on F(2) and F values, respectively. Anisotropic temperature factors were employed for all six non-H atoms and fixed isotropic temperature factors for the two H atoms. The structure contains zigzag chains of hydrogen-bonded anion tetrahedra that extend in the [010] direction. Each tetrahedron is additionally linked to a tetrahedron in a neighboring chain to give a planar structure with hydrogen-bonded sheets lying parallel to (101). Thermal analysis of the superprotonic transition in Cs_2(HSO_4)(H_2PO_4) showed that the transformation to the high-temperature phase occurs by a two-step process. The first is a sharp transition at 334 K and the second a gradual transition from 342 to 378 K. The heat of transformation for the entire process (~330-382 K) is 44 \u00b1 2 J g^(-1). Thermal decomposition of Cs_2(HSO_4)(H_2PO_4) takes place at much higher temperatures, with an onset of approximately 460 K.",
"doi": "10.1107/S0108768199009921",
"issn": "0108-7681",
"publisher": "International Union of Crystallography",
"publication": "Acta crystallographica. Section B, Structural science",
"publication_date": "1999-12",
"series_number": "6",
"volume": "55",
"issue": "6",
"pages": "937-946"
}
]