WO2003012894A2 - Electrolytes acides solides pour dispositifs electrochimiques - Google Patents

Electrolytes acides solides pour dispositifs electrochimiques Download PDF

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WO2003012894A2
WO2003012894A2 PCT/US2002/024564 US0224564W WO03012894A2 WO 2003012894 A2 WO2003012894 A2 WO 2003012894A2 US 0224564 W US0224564 W US 0224564W WO 03012894 A2 WO03012894 A2 WO 03012894A2
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solid acid
charge
electrolyte
transition metal
electrolyte membrane
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WO2003012894A3 (fr
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Sossina M. Haile
Calum Chisholm
Ryan B. Merle
Dane Boysen
Sekharipuram R. Narayanan
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California Institute of Technology
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California Institute of Technology
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Priority to JP2003517965A priority Critical patent/JP4754782B2/ja
Priority to EP02768403A priority patent/EP1423887A4/fr
Priority to AU2002330966A priority patent/AU2002330966A1/en
Publication of WO2003012894A2 publication Critical patent/WO2003012894A2/fr
Publication of WO2003012894A3 publication Critical patent/WO2003012894A3/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
    • H01M10/0562—Solid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00—Primary cells; Manufacture thereof
    • H01M6/14—Cells with non-aqueous electrolyte
    • H01M6/18—Cells with non-aqueous electrolyte with solid electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
    • H01M2300/0068—Solid electrolytes inorganic
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to electrolytes for electrochemical devices, methods of synthesizing such materials, and electrochemical devices incorporating such materials; and more particularly to electrolytes made from novel solid acid materials.
  • Electrochemical devices depend on the flow of protons, or the flow of both protons and electrons, through a proton conducting material, such as a membrane. Accordingly, materials which conduct protons, or both protons and electrons, have applications as electrolytes or electrodes in a number of electrochemical devices including fuel cells, electrochemical or supercapacitors, sensors, hydrogen separation membranes and membrane reactors.
  • Fuel cells are attractive alternatives to combustion engines for a wide variety of applications, because of their higher .efficiency and the lower level of pollutants produced from their operation.
  • DMFC direct methanol fuel cell
  • the operating efficiency of the device is limited by the efficiency of the electrolyte at transporting protons.
  • perflourinated sulphonic acid polymers, polyhydrocarbon sulfonic polymers, and composites thereof are used as electrolyte membrane materials for fuel cell.
  • these conventional materials utilize hydronium ions (HsO + ) to facilitate proton conduction. Accordingly, these materials must be hydrated, and a loss of water immediately results in degradation of the conductivity of the electrolyte and therefore the efficiency of the fuel cell. Moreover, this degradation is irreversible, i.e., a simple reintroduction of water to the system does not restore the conductivity of the electrolyte.
  • fuel cells utilizing these materials require peripheral systems to ensure water recirculation and temperature control to keep the water from evaporating. Not only do these systems increase the complexity and cost of these fuel cells, but because the system cannot exceed a temperature of 100 °C the fuel cell catalysts and other systems cannot be operated a maximum efficiency. Higher temperatures would also reduce carbon monoxide poisoning of the fuel cell catalyst.
  • CsHSO solid acids
  • the electrolyte in fuel cells operated at temperatures of 140-160 °C.
  • Use of this material greatly simplifies fuel cell design relative to polymer electrolyte fuel cells because hydration of the electrolyte is not necessary and, because of the elevated temperature of operation, residual CO in the fuel stream can be better tolerated.
  • the high conductivity of CsHSO and analogous materials results from a structural phase transition that occurs at 141 °C from an ordered structure, based on chains of SO groups linked by well-defined hydrogen bonds, to a disordered structure in which SO 4 groups freely reorient and easily pass protons between one another.
  • disorder in the crystal structure is a key prerequisite for high proton conductivity.
  • solid acid electrolytes may solve many of the problems facing state-of-the-art polymer based fuel cells. These problems include inability to operate at temperatures above 100°C (which would increase the CO tolerance of the Pt catalyst), humidification requirements, and methanol permeation across the electrolyte. The technological objectives of this work are thus to simply fuel cell operation by use of alternative electrolytes. However, the lifetime of these sulfate and selenium based solid acids is insufficient for commercial applications. The poor lifetime of both CsHSO 4 and CsHSeO 4 under fuel cell operating conditions results from the reduction of sulfur and selenium by hydrogen in the presence of typical fuel cell catalysts, according to:
  • the present invention is directed to a stable electrolyte material comprising a solid acid capable of forming hydrogen bonds and undergoing rotational disorder capable of extended operation at elevated temperatures, such as, for example, solid acids having a tetrahedral or octahedral hydrogen bonding anion group; a superproto ic trigonal disordered phase; and/or being capable of operating at temperatures of -100 °C.
  • the current invention is directed to several classes of improved solid acid electrolyte materials, methods of synthesizing such materials, and electrochemical devices incorporating such materials.
  • the invention is directed to an electrolyte comprising a solid acid having a superprotonic trigonal phase.
  • the solid acid may be chosen from phosphate species of the general form: (M x M' ⁇ - )3H3x(PO 4 )2, where M is any alkali or transition metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH 4 + ; and M' is any alkaline earth or transition metal having a +2 charge, such as Mg 2+ ...Ba 2+ , Pb 2+ .
  • the solid acid may directed to a mixed phosphate compound having the general form: M3H2 [(Pi- x ,Si x )O4]2 or M3H2 [(P 1 -x,Ge ⁇ )O 4 ]2 where M is any alkaline or transition metal having a +2 charge, such as Mg 2+ ...Ba 2+ , Pb 2+ .
  • the invention is directed to an electrolyte comprising a solid acid having a tetrahedral anion chosen from the group PO 4 , PO3F and PO3H.
  • the solid acid may be of the general form: MH 1+x (PO 3 A) 1- ⁇ (P ⁇ 4) x and M 3 Hx[(P ⁇ 3A) ⁇ (P ⁇ 4) ⁇ -x]2, where M is any alkali metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH 4 + , and A is F or H.
  • the solid acid species may be chosen from monofluorophosphate and phosphite species or from mixed monoflurophosphate/phosphate and mixed phosphite/phosphate species.
  • the solid acid species may also be chosen from molecules having mixed chromate/phosphate tetrahedral anion species. Such molecules have the general form: MH 1+ ⁇ (Cr ⁇ 4) ⁇ -x(PO 4 ) x and M 3 Hx[(Cr ⁇ 4)x(P ⁇ 4) ⁇ - x ]2, where M is any alkaline metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH 4 + .
  • the invention is directed to an electrolyte comprising a solid acid having an octahedral anion.
  • the solid acid may be chosen from fluorosilicates and germanates of the general form: MHSiF ⁇ and MHGeF ⁇ , where M is any alkaline metal or other functional group having a +1 charge, such as, Li + ... Cs + , NH 4 + .
  • the solid acid may also be chosen from mixed phosphosilicates and phosphogermanates of the general form: MH ⁇ (P ⁇ - x Si ⁇ )F6 and MH x (P 1 . ⁇ Ge x )F6, where M is any alkaline metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH4 + .
  • the solid acid may also be chosen from compounds with aluminum flouride octahedral anion groups AlF ⁇ .
  • the invention is directed to a membrane comprising the solid acid electrolyte.
  • the invention may further comprise a structural binder or matrix material to enhance the mechanical integrity and/or chemical stability of the membrane.
  • the binder may comprise any suitable stabilizing material, such as, for example a polymer, a ceramic, or an oxide glass.
  • the invention is directed to an electronically conducting matrix material, such as a metal or a carbon based material.
  • the invention is directed to methods of synthesizing the solid acids according to the current invention.
  • the invention is directed to an electrochemical device incorporating the solid acid electrolyte.
  • the electrolyte may be incorporated into any electrochemical device requiring a flow of either protons or protons and electrons across a membrane to function, such as, for example, a fuel cell, a hydrogen separation membrane, or an electrolysis cell.
  • Figures la to le show graphical representations of the properties of an exemplary CsH(POsH) solid acid according to the current invention
  • Figure 2 shows a graphical representation of the temperature decomposition properties of exemplary solid acid electrolytes under nitrogen according to the current invention
  • Figure 3 shows a graphical representation of the conductivity properties of exemplary solid acid electrolytes under air according to the present invention
  • Figure 4 shows a graphical representation of the conductivity properties of exemplary solid acid electrolytes according to the present invention
  • Figure 5 shows a graphical comparison of the decomposition properties of conventional (CSHSO ) and exemplary solid acid electrolytes under hydrogen according to the present invention
  • Figure 6 shows a graphical comparison of the decomposition properties of conventional (CsHSO 4 ) and exemplary solid acid electrolytes under vapor phase methanol according to the present invention
  • Figure 7 shows a graphical representation of the temperature decomposition properties of exemplary solid acid electrolytes under nitrogen synthesized according to the current invention
  • Figure 8 shows a graphical representation of the conductivity properties of exemplary solid acid electrolytes synthesized according to the current invention
  • Figure 9 shows a graphical representation of the conductivity properties of exemplary solid acid electrolytes synthesized according to the current invention.
  • Figures 10a and 10b show a pictorial reproduction of exemplary membranes made of exemplary solid acid electrolytes according to the current invention
  • Figure 11 shows a schematic of an exemplary hydrogen/air fuel cell using an exemplary solid acid electrolyte membrane according to the current invention
  • Figure 12 shows a schematic of an exemplary direct methanol fuel cell using an exemplary solid acid supported by a binder according to the current invention
  • Figure 13 shows a schematic of another exemplary hydrogen separation membrane using an exemplary protcn conducting solid acid according to the current invention
  • Figure 14 shows a schematic of an exemplary hydrogen separation membrane using an exemplary mixed electron and proton conducting solid acid according to the current invention
  • I Figure 15 shows a schematic of an exemplary embodiment of a membrane reactor using an exemplary solid acid according to the current invention.
  • the present invention is directed to a stable electrolyte material comprising a solid acid capable of forming hydrogen bonds and undergoing rotational disorder and capable of extended operation at elevated temperatures,
  • solid acids having a tetrahedral or octahedral hydrogen bonding anion group; a superprotonic trigonal, tetragonal or cubic disordered phase; and/or being capable of operating at temperatures of 100 °C and higher.
  • solid acids having a tetrahedral or octahedral hydrogen bonding anion group
  • superprotonic trigonal, tetragonal or cubic disordered phase and/or being capable of operating at temperatures of 100 °C and higher.
  • solid acid electrolytes or “electrolytes” herein.
  • solid acids used herein refers to compounds which have properties that are intermediate between those of a normal acid, such as, H2SO4, and a normal salt, such as, CS2SO4.
  • a normal acid such as, H2SO4
  • a normal salt such as, CS2SO4.
  • chemical formula of the solid acids of the type used according to the present invention can be written as a
  • Solid acids generally comprise oxyanions, such as, for example, SO4, SO3, Se ⁇ ,
  • the structure may contain more than one type of oxy anion XO4, XO3 XO3A or XF ⁇ group, and may also contain more than one type of cation M species.
  • solid acids the proton transport mechanism does not rely on the motion of hydroniu ions.
  • solid acids do not need to be hydrated to function and can be operated at elevated temperatures to increase efficiency and reduce the potential for poisoning contamination of the catalyst medium in the electrochemical device.
  • the current invention is directed to improved solid acid structures which do not suffer from reduction in the presence of catalytic materials such as Pt and other transition metal elements.
  • catalytic materials such as Pt and other transition metal elements.
  • any sohd acids having a tetrahedral or octahedral hydrogen bonding anion group; a superprotonic trigonal disorder phase; and/or being capable of operating at temperatures of ⁇ 100 °C in the presence of typical fuel cell catalysts may be utilized as an electrolyte material in the current invention.
  • Applicants have discovered that by replacing the Sulfur (or Se) of superprotonic solid acids with elements such as Si and Ge the reduction reaction can be avoided because analogous reduction compounds such as HiSi and H4Ge are extremely unstable.
  • superprotonic acids such as LaHSi ⁇ 4, BaH 2 SiO4, and SrH 2 GeO 4 etc. are preferably used in the devices and materials of the current invention.
  • the invention is directed to a solid acid having a disordered trigonal phase and a tetrahedral anion.
  • a disordered trigonal phase and a tetrahedral anion for example, it is well known that the compounds Pbs(PO )2 and RbsH(SeO )2 are essentially isostructural at room temperature, with the exception of incorporated protons in the selenate compound. Upon heating, both undergo a transition to a disordered, trigonal phase. Because of the incorporation of protons into the selenate, this disorder is accompanied by an increase of protonic conductivity by several orders of magnitude.
  • the solid acid electrolyte is chosen from the phosphate species of the general form: (Mi- x M' x )3H3(PO )2, where M is any alkaline earth or transition metal having a +2 charge, such as Mg 2+ ...Ba 2+ , Pb 2+ ; and M' is any alkali metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH4 + .
  • protons are introduced into the trigonal compounds such as Pbs(PO4)2 by substituting species such as Si 4+ and Ge 4+ for the P 5+ .
  • the reduction in positive charge can then be balanced by incorporated protons.
  • suitable sohd acids can be chosen from the group described by the form: M3H2 [(P ⁇ -x,Si x )O 4 ]2 and M3H2 [(Pi-x,Ge x )O4] where M is any alkali or transition metal having a +2 charge, such as Mg 2+ ...Ba2+, Pb 2+ .
  • the tetrahedral anion group, POsF is utilized. It is well- known that PO3F, is isoelectronic with SO4, and also shares chemical properties. For example, the compound CSHPO3F is known in the literature, and has a room temperature structure which shares some similarities to the superprotonic tetragonal structure of CsHSO4.
  • the proton content in monofluorophosphate solid acids can be increased by introducing phosphate anions according to the general chemical formula MH 1 + ⁇ (P ⁇ 3F) ⁇ -x (PO4) x , which includes the simple compounds MHPO3F, in analogy to known MHi+ x (SO4)i-x(PO4)x compounds.
  • the PO3F anion can be utilized to replace SO 4 not only in compounds of general stoichiometry MHSO4, but also in those with stoichiometry MsH(SO4)2.
  • the solid acid may be chosen from monofluorophosphate and mixed monofluorophosphate/phosphate species of the general form: M 8 H(PO3F)2 and M3H ⁇ +2x[(P ⁇ 3F) 1 . x (P ⁇ 4)x]2, where M is any alkali metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH4 + .
  • Still another type of tetrahedral group that can be considered a viable substitute for SO4 (or Se ⁇ 4) is PO3H.
  • the chemical similarity between SO4 and PO ⁇ H, is somewhat less than that between SO 4 and PO3F, because the P-H bond is quite distinct. Nevertheless, the room temperature structures are built on similar hydrogen bonded tetrahedral units.
  • MH(PO 3 H) family including CSH2PO3, KH2PO3, LLH2PO3 and NH4H2PO3. In comparison to compounds such as CSH2PO4, it is noteworthy that the oxidation state is +3 rather than +5, and thus the phosphites are unlikely to be susceptible to reduction during fuel cell operation.
  • the tetrahedral solid acid species may be chosen from mixed phosphite and phosphite/phosphate species of the general form: MH(PO 3 H), M 3 H(PO 3 H) 2j MH 1+ ⁇ (PO 3 H) ⁇ . ⁇ (P ⁇ 4)x 5 and M 8 Hi + 2x[(PO 3 H)i. x (PO4)j2 where M is any alkali metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH + .
  • the conductivity in the high temperature phase at 160 °C is 5.5 x 10 -3 ⁇ c ⁇ r 1 , and the activation energy for proton transport is 0.40 ⁇ 0.01 eV, as shown by comparison in Figures Id and le. These values suggest that proton transport is facilitated by rapid PO3H group reorientations in the cubic phase of CsH(POaH), as is known to occur in the high temperature, tetragonal phase of CsHSO4.
  • Still another type of solid acid electrolyte material having a tetrahedral anion is formed by K2CrO 4 demonstrating the interchangeable nature of sulfates and chromates. Chromates have also been shown to exhibit the same tetrahedral disorder at elevated temperatures that sulfates do, and therefore, the tetrahedral solid acid species may also be chosen from the mixed chromate species of the general form: MH 1 + x (CrO4)i-x(PO4)x, where M is any alkaline metal or other functional group having a +1 charge, such as, Li + ... Cs + , NH4 "1" .
  • the invention is directed to solid acid electrolyte compounds that contain an octahedral polyanion.
  • materials such as KPF ⁇ form structures in which disorder is sustained at slightly elevated temperature.
  • such materials contain no protons.
  • protons can be introduced for charge balance reasons.
  • the solid acid may be chosen from fluorosilicates and germanates of the general form: MHSiF ⁇ and MHGeF ⁇ , where M is any alkaline metal or other functional group having a +1 charge, such as, Li + ... Cs + , NH 4 .
  • the known structural transition in compounds such as KPF ⁇ to a disordered state can be taken advantage of for proton transport by partial (rather than complete) chemical substitution of the PF ⁇ anion by SiF ⁇ or GeF ⁇ . Because proton incorporation accompanies the substitution, high conductivity in the high-temperature disordered phase can be obtained. + .
  • the sohd acid electrolyte material may be chosen from mixed phosphosilicates and phosphogermanates of the general form: MH x (P ⁇ - x Si x )F6 and MH x (P ⁇ - x Ge x )F6, where M is any alkaline metal or other functional group having a +1 charge, such as, Li + ... Cs + , NH 4 + .
  • the solid acid may have an octahedral anion group according to: AlF ⁇ .
  • Exemplary embodiments of such compounds would be MH2AIF6 and M2HAIF6, where M is any alkaline metal or other functional group having a +1 charge, such as, Li + ...Cs + , NH 4 + ; or M'HAlF ⁇ , where M 1 is +2, where M' is any alkali or transition metal having a +2 charge, such as Mg 2+ ...Ba 2+ , Pb 2+ .
  • Other embodiments would also include mixtures of the above species with MHSiFe, MHGeFe and MPF 6 .
  • the preferred material for any specific electrochemical device depends on the application.
  • the preferred species may depend on the needs of a device, such as, high conductivity, low cost, thermal stability or chemical stability, etc.
  • solid acid electrolytes can be made to conduct both electrons and protons depending on the choice of the M cation and the X element in the anion XO4, XO3 or XFG portion of the above chemical formulae.
  • a variable valence element such as, Pb or In for M, or Cr or Mn for X
  • the solid acid can be made to conduct electrons as well as protons.
  • the invention is also directed to methods of forming the superprotonic solid acid electrolyte materials described above.
  • the synthesis of the stable, high-conductivity solid acid compounds derives from the Applicants' recognition that degradation of conventional solid acid materials, such as CsHS0 4 occurs via the reduction of sulfur under hydrogen to yield H 2 S. This reduction reaction is normally slow, even at fuel cell operation temperatures of ⁇ 100°C, however, it is highly accelerated in the presence of typical fuel cell catalysts.
  • target analogies to CsHSO4 and CSH2PO4 are, for example, LaHSiO4 and BaH 2 SiO4, etc.
  • one method of synthesizing such solid acid electrolyte materials begins with the synthesis of known acid silicates and germanates. Most such compounds contain small alkali or alkaline earth ions. In order to prepare crystalline compounds incorporating large cations (which are necessary for high proton conductivity) the same synthesis procedures are followed with the exception that one or more of the reactant materials is changed, for example, replacing NaOH with CsOH to yield a cesium acid silicate or germanate.
  • an ion exchange reaction is carried out on known compounds. That is, Na can be replaced in a known acid silicate with Cs by soaking the original material in molten CsOH.
  • compounds containing Li rather than H are formed, and then an ion exchange reaction is carried out in an acid media.
  • the compound LaLiSiO4 is known, the lithium can be replaced with protons using an acid that will not dissolve the base material.
  • CsH(PO3H) The compound CsH(PO3H) was synthesized from aqueous solutions of cesium carbonate and phosphorous acid in which the Cs:PO3H mole ratio was fixed at 1:1. Just enough water was added to ensure complete dissolution, and then the solution gently heated to induce H2O evaporation and precipitation of the product. The resultant material was separated from the mother liquor by filtering and rinsed with acetone.
  • NaCaHSiO 4 combine NaOH, Ca(OH) 2 and SiO 2 (in a 3:2:2 molar ratio) with a few drops of water and place in a thermal bomb at 280°C for 48 hours.
  • SrH2Ge ⁇ 4 combine Sr(OH) 2 and GeO 2 (in a 1:1 molar ratio) and place in a thermal bomb at 280°C for several days; or, mix Sr(OH)2 and GeO 2 (in a 1:1 molar ratio) in hot water to induce formation of the desired product.
  • the remaining two compounds, NaCaHSiO 4 and SrH 2 GeO4 were characterized by the Applicants by thermal methods (thermogravimetry and calorimetry) and all four compounds were examined by impedance spectroscopy to evaluate their suitability as fuel cell electrolytes.
  • thermal methods thermogravimetry and calorimetry
  • impedance spectroscopy to evaluate their suitability as fuel cell electrolytes.
  • H/D ion exchange and subsequent conductivity measurements were additionally performed to establish the nature of the charge-carrying species.
  • the total weight change of 9.6 % corresponds to 1.2 moles of H 2 O (per mole SrH2GeO 4 ). That this value is greater than the expected value of 8.0 % (1 mole H2 ⁇ /SrH 2 Ge ⁇ 4 ) suggests that the initial weight loss over the temperature range 70 - 295 °C of 1.6 wt % corresponds to the loss of surface water.
  • the first material is thermally stable to 800 °C (with the exception of a small weight loss due to the desorption of surface water adsorbed post- synthesis), which is consistent with the absence of acid protons.
  • the second material is thermally stable to only ⁇ 400 °C, consistent with the presence of acid protons.
  • the ion exchange methods (which have led to an increase in the conductivity of NaCaHSiO4 by two orders of magnitude) show excellent results.
  • the solid acid electrolyte materials of the current invention are preferably formed into membranes (ME As). Accordingly, this invention is also directed to methods of fabricating membranes from the solid acid electrolyte materials described herein.
  • Fabrication of thin, high density solid acid membranes generally entails the simultaneous application of high temperatures and pressures (uniaxial). Applicants have found that application of pressures of ⁇ 700 psi and temperatures of ⁇ 190°C yield transparent membranes of CsHSO4, as shown in Figures 10a and 10b. Specifically, Figure 10a shows the image of hot, pressed CsHSO 4 with a sample thickness of 320 ⁇ m mounted in copper plate under reflected light, and Figure 10b shows the material with light shining from behind emphasizing translucency.
  • the solid acid electrolyte materials are processed as a composite in which the solid acid is embedded in a supporting matrix.
  • the solid acid is in its superportonic state, exhibits high conductivity, and provides the desired electrochemical properties
  • the support matrix provides mechanical support, and it may also serve to protect the solid acid from water in the environment.
  • any suitable matrix material may be utilized which would provide sufficient mechanical and/or chemical support, such as, for example, a polymer, a ceramic, or an oxide glass.
  • composite membrane of solid acids according to the invention and a simple structural polymer, such as polyvinylidene fluoride may be prepared by simple melt-processing, where the two components are lightly ground together and then hot-pressed at 180 °C and 10 kpsi for 15 minutes.
  • the greatest difficulty often encountered with this method is in removing the electrolyte from the hot press without introducing cracks, and the method has a limitation that the thinnest membranes that can be fabricated by the method of hot-pressing is ⁇ 200 ⁇ m.
  • the mixture of the two components is then hot pressed, preferably at a temperature which causes the solid acid to melt and flow, to yield a dense composite membrane.
  • the invention is directed to a method of forming thinner electrolytes in a stabilizing matrix.
  • the membrane may be formed by providing a thermoset polymer in a monomer or prepolymer form and then polymerizing the polymer in situ with the solid acid. In this method, the two materials are again ground together and the polymerization crosslinking catalyst agent is added. Any suitable prepolymer may be used, such as, for example, polyester resins.
  • a solid acid was ground and mixed with the prepolymer. The polymerization catalyst was introduced and the mixture then poured onto a plate and pressed into a thin film. The film thus produced was then cured at 100 °C for approximately 2 hours.
  • the membrane may be formed by suspension casting.
  • the sohd acid and matrix material are dissolved and/or dispersed in an appropriate solvent system, such as a water/ethanol solution.
  • the membrane is then formed by casting the suspension and allowing the solvents to evaporate.
  • membranes containing non-polymeric matrix materials such as ceramic or oxide glass, can be formed by this method.
  • the solid acid is mixed with a supporting structure that is electrochemically unreactive, to form a composite material.
  • the solid acids of the current invention without judicious selection of the M and X species, are inherently poor conductors of electrons, these materials alone may only be utilized to provide proton transport.
  • the matrix material has conducting properties such that the composite membrane provides both electron and proton transport.
  • electronic conductivity is introduced into the solid acid by preparing a composite, via any of the above methods, comprised of the solid acid and a second substance which has a high electronic conductivity.
  • This second substance may any suitable electronically conducting material, such as, for example, a conducting polymer, such as polyaniline; or a typical metal, such as copper; or graphite.
  • a conducting polymer such as polyaniline
  • a typical metal such as copper
  • graphite such as copper
  • electronic conductivity is introduced into the solid acid by direct chemical substitution with variable valence ions as described earlier.
  • variable valence ions for example, a portion of the phosphorous, silicon or germanium might be replaced with ions that exhibit variable valence states, such as manganese.
  • ions that exhibit variable valence states such as manganese.
  • alkali or alkaline earth metals might be replaced with large variable valence ions such as thallium, indium, lead and tin.
  • the solid acid I so modified may be used in an electrochemical device directly or may be combined with a supporting matrix material as a composite as discussed above.
  • the present invention is also directed to electrochemical devices incorporating such materials and membranes. Embodiments of some exemplary devices are shown in Figures 11 to 15.
  • Figures 11 and 12 show exemplary embodiments of a hydrogen/air fuel cell and a methanol fuel cell 10, in which the proton conducting membrane 12 is a solid acid electrolyte, alone or in composite form, of the type described herein sandwiched between two graphite layers 14. Because the membrane 12 need not
  • the fuel cell system can be quite simple. For example, as shown, no humidification system, normally required for conventional fuel cell utilizing conventional electrolyte materials such as Nafion, is required. In addition, less rigid temperature monitoring and control may be used in the fuel cell. Because the solid acid based membrane need not be humidified, the fuel cell
  • solid acid electrolyte materials in fuel cells are an important application, such materials may also be incorporated into various membrane reactors.
  • the Pt-based catalyst 16 in the hydrogen/air fuel cell shown in Figure 11 is very sensitive to CO poisoning, particularly at
  • the hydrogen produced by the reformer is often cleaned of CO impurities before it enters the fuel cell. Accordingly, in one embodiment, shown schematically in Figure 13, the material is shown incorporated into a hydrogen separation 5 membrane for the removal of CO and other gases from hydrogen.
  • the hydrogen separation membrane 20 is made of a proton conducting electrolyte 22 of the type described herein, and is connected to a current source 24. Hydrogen gas 26, mixed with other undesirable gases 27, is introduced onto one side (inlet) 28 of the membrane and clean hydrogen gas 26a is extracted from the other side of the membrane.
  • application of current causes the hydrogen gas to dissociate into H + and Because the membrane conducts only protons, these protons are the only species which can migrate through the membrane.
  • the electrons migrate through the current source to the outlet side 29 of the membrane, where the H + combines with electrons from the current source to form hydrogen gas.
  • Such membranes are substantially impervious to other gases and fluids. This overall hydrogen separation process is driven by the electric current applied from the current source 24.
  • the hydrogen separation membrane 30 is made of a mixed proton and electron conducting membrane 36.
  • a membrane might be made by including, for example, a given amount of a variable valence element, such as, Cr or Mn for X, to the solid acid, as described above.
  • the membrane may be made as a composite in which the matrix substance may be an electronically conducting material, such as a conducting polymer, such as polyaniline, or a typical metal, such as aluminum or copper, or graphite.
  • the membrane of the current invention may be 5 used in other reactions which utilize either a proton or a mixed proton and electron conducting membrane, such as, for example, in selective hydrogenation reactions.
  • specific embodiments are disclosed herein, it is expected that persons skilled in the art can and will design solid acid electrolytes and electrochemical devices utilizing such materials that are within the scope of the following description either literally or under the Doctrine of Equivalents.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • General Chemical & Material Sciences (AREA)
  • Electrochemistry (AREA)
  • Sustainable Energy (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Conductive Materials (AREA)
  • Silicates, Zeolites, And Molecular Sieves (AREA)
  • Electric Double-Layer Capacitors Or The Like (AREA)
  • Secondary Cells (AREA)

Abstract

La présente invention concerne des matériaux pour des électrolytes acides solides améliorés, des procédés de synthèse de tels matériaux, et des dispositifs électrochimiques incorporant de tels matériaux. Le matériau d'électrolyte stable comporte un acide solide capable d'être soumis à une déformation rotationnelle de groupes d'oxyanions et capable de fonctionnement prolongé à des températures élevées. C'est à dire, des acides solides comprenant des groupes anioniques à liaisons d'hydrogène; une phase superprotonique déformée trigone, tétragone, ou cubique; et capable de fonctionner à des températures d'au moins ∩100 °C.
PCT/US2002/024564 2001-08-01 2002-08-01 Electrolytes acides solides pour dispositifs electrochimiques Ceased WO2003012894A2 (fr)

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JP2003517965A JP4754782B2 (ja) 2001-08-01 2002-08-01 電気化学デバイスのための固体酸電解質
EP02768403A EP1423887A4 (fr) 2001-08-01 2002-08-01 Electrolytes acides solides pour dispositifs electrochimiques
AU2002330966A AU2002330966A1 (en) 2001-08-01 2002-08-01 Solid acid electrolytes for electrochemical devices

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US30980701P 2001-08-01 2001-08-01
US60/309,807 2001-08-01
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CN112563564A (zh) * 2020-11-13 2021-03-26 上海空间电源研究所 一种制备钠离子固体电解质的软化学合成方法

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JP2007531971A (ja) * 2004-03-30 2007-11-08 カリフォルニア・インスティチュート・オブ・テクノロジー 固体酸電解質を使用する直接型アルコール燃料電池
JP2007123833A (ja) * 2005-09-30 2007-05-17 National Institute Of Advanced Industrial & Technology 固体酸塩の活性化方法及びこれを用いた大容量キャパシター並びに燃料電池
JP2008084788A (ja) * 2006-09-28 2008-04-10 Sanyo Electric Co Ltd 電解質膜、その製造方法および燃料電池
JP5303838B2 (ja) * 2007-01-22 2013-10-02 凸版印刷株式会社 プロトン伝導性材料、それを用いて成る膜電極接合体（ｍｅａ）およびその製造方法
JP5381639B2 (ja) * 2009-11-20 2014-01-08 富士電機株式会社 固体電解質形燃料電池およびその製造方法
JP2011138688A (ja) * 2009-12-28 2011-07-14 Fuji Electric Co Ltd 燃料電池
JP5811191B2 (ja) * 2011-12-28 2015-11-11 株式会社村田製作所 全固体電池およびその製造方法
JP6998586B2 (ja) * 2017-11-08 2022-02-10 国立大学法人広島大学 プロトン伝導体及びその製造方法

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CN112563564A (zh) * 2020-11-13 2021-03-26 上海空间电源研究所 一种制备钠离子固体电解质的软化学合成方法
CN112563564B (zh) * 2020-11-13 2021-11-09 上海空间电源研究所 一种制备钠离子固体电解质的软化学合成方法

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EP1423887A4 (fr) 2009-08-12
AU2002330966A1 (en) 2003-02-17
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JP4754782B2 (ja) 2011-08-24
JP2004537834A (ja) 2004-12-16

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