CA1305751C - Solid compositions for fuel cells, sensors and catalysts - Google Patents
Solid compositions for fuel cells, sensors and catalystsInfo
- Publication number
- CA1305751C CA1305751C CA000553723A CA553723A CA1305751C CA 1305751 C CA1305751 C CA 1305751C CA 000553723 A CA000553723 A CA 000553723A CA 553723 A CA553723 A CA 553723A CA 1305751 C CA1305751 C CA 1305751C
- Authority
- CA
- Canada
- Prior art keywords
- solid material
- electrolyte
- lanthanum
- independently selected
- solid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- 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
- H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
- H01M8/124—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte characterised by the process of manufacturing or by the material of the electrolyte
- H01M8/1246—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte characterised by the process of manufacturing or by the material of the electrolyte the electrolyte consisting of oxides
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
- H01M4/9025—Oxides specially used in fuel cell operating at high temperature, e.g. SOFC
- H01M4/9033—Complex oxides, optionally doped, of the type M1MeO3, M1 being an alkaline earth metal or a rare earth, Me being a metal, e.g. perovskites
-
- 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
- H01M2300/0071—Oxides
- H01M2300/0074—Ion conductive at high temperature
-
- 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
-
- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Life Sciences & Earth Sciences (AREA)
- Sustainable Development (AREA)
- Sustainable Energy (AREA)
- Inert Electrodes (AREA)
- Fuel Cell (AREA)
Abstract
SOLID COMPOSITIONS FOR
FUELS, SENSORS AND CATALYSTS
ABSTRACT OF THE INVENTION
The present invention relates to solid materials for use as electrolyte for a fuel cell, or for a sensor, or as a catalyst. Rep-resentative structures include lanthanum fluoride, lead potassium fluoride, lead bismuth fluoride, lanthanum strontium fluoride, lanthan strontium lithium fluoride, calcium uranium, cesium fluoride, PbSnFy, KSn2F4, SrCl2?KCl, LaOF2, PbSnF8?PbSnO, lanthanum oxyfluoride, oxide, calcium fluoride, SmNdFO, and the like. In another aspect, the present invention relates to a composite and a process to obtain it of the formula:
A1-yByQO3 having a perovskite or a perovskite-type structure as an electrode catalyst in combination with:
AyB1-yF2+y as a discontinuous surface coating solid electrolyte solid electrolyte wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, and scandium, B is independently selected from strontium, calcium, barium or magnesium, Q is independently selected from nickel, cobalt, iron or manganese, and y is between about 0.0001 and 1, which process comprises:
(a) obtaining a particulate of:
A1-yByQO3 wherein A, B and y are defined hereinabove having an average size distribution of between about 50 and 200 Angstroms In diameter:
(b) reacting the particle of step (a) with a vapor comprising:
AyB1-yF2+y wherein A, B and y are defined hereinabove at about ambient pres-sure at between about 0 and 1000°C: for between about 10 and 30 hr.
obtain a composite of between about 25 to 1000 microns in thickness:
(c) recovering the composite of step (b) having multiple inter-faces between the electrode and electrolyte.
In another aspect the invention relates to the heating of these solid materials with oxygen and water to obtain higher ionic conductivity. In another aspect the invention relates to the elec-trochemical doping of oxide ions present by treatment of the elec-trode-lanthanum fluoride interface at between about 0 and 400°C in an oxygen environment at between about 10-3 and 10-6 amperes per square centimeter for between about 1 and 60 minutes.
The invention also includes the use of the fuel cells disclosed to generate electricity.
FUELS, SENSORS AND CATALYSTS
ABSTRACT OF THE INVENTION
The present invention relates to solid materials for use as electrolyte for a fuel cell, or for a sensor, or as a catalyst. Rep-resentative structures include lanthanum fluoride, lead potassium fluoride, lead bismuth fluoride, lanthanum strontium fluoride, lanthan strontium lithium fluoride, calcium uranium, cesium fluoride, PbSnFy, KSn2F4, SrCl2?KCl, LaOF2, PbSnF8?PbSnO, lanthanum oxyfluoride, oxide, calcium fluoride, SmNdFO, and the like. In another aspect, the present invention relates to a composite and a process to obtain it of the formula:
A1-yByQO3 having a perovskite or a perovskite-type structure as an electrode catalyst in combination with:
AyB1-yF2+y as a discontinuous surface coating solid electrolyte solid electrolyte wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, and scandium, B is independently selected from strontium, calcium, barium or magnesium, Q is independently selected from nickel, cobalt, iron or manganese, and y is between about 0.0001 and 1, which process comprises:
(a) obtaining a particulate of:
A1-yByQO3 wherein A, B and y are defined hereinabove having an average size distribution of between about 50 and 200 Angstroms In diameter:
(b) reacting the particle of step (a) with a vapor comprising:
AyB1-yF2+y wherein A, B and y are defined hereinabove at about ambient pres-sure at between about 0 and 1000°C: for between about 10 and 30 hr.
obtain a composite of between about 25 to 1000 microns in thickness:
(c) recovering the composite of step (b) having multiple inter-faces between the electrode and electrolyte.
In another aspect the invention relates to the heating of these solid materials with oxygen and water to obtain higher ionic conductivity. In another aspect the invention relates to the elec-trochemical doping of oxide ions present by treatment of the elec-trode-lanthanum fluoride interface at between about 0 and 400°C in an oxygen environment at between about 10-3 and 10-6 amperes per square centimeter for between about 1 and 60 minutes.
The invention also includes the use of the fuel cells disclosed to generate electricity.
Description
~3~5~5~
SOLID COMPOSITIONS FC)R
FUEI CELLS SENSORS AND CATALYSTS
. _____ BACKGROUND OF THE INVENTION
Fi~ d ~f the In~n~ G~
The present invention relates ~:o materlals and processes to prepare polycrystal and monocrystal forms for use in fuel cells in sensors and as catalys~s. In specific embodiments, a fuel cell having oxygenlsolid lanthanum fluoride (as a single crystal)/hydrogen configuration produces about 1 volt of open circuit potential at 10 essentially ambient temperature. In other speciflc embodiments, specific mixed lanthanide or alkaline earth fluorides also produce electricity at moderate: temperatures. Embodiments also include a porous perovskite-type metallic transition metal oxide electrode and a lanthanum metailalkaline earth/fluoride elec~rolyte which are useful as 15 a soild electrode/electrolyte in a fuel cell, as a sensor, or as a catalyst .
DES:CRIPTII:)N OF THE RELEVANT ART
Fuel cells convert chemical energy :to electrical energy directly, without ~ having a Carnot-cycle effic~ency limitat~on, through 20 electrochemica! oxidation-reduct10n reactions of fuels. Several types of fuel cells have been or are being investigated at the present time.
;
, ~ ~,J
. . ,, ~, . .
The solid electrolyte fuel cell which can be considered as the third generation fuel cell technology, i~ essentially an oxygen-hydrogen (or H2-C0 mixture~ fuel cell operated at high temperature lca. 1000C) ~ith a solid ceramic oxide material used as S the electrolyte. At present, yttrium- or calcium-stabilked zirconium oxides have been used as the electrolyte. The mechanism of ionic conduction is oxygen ion transport via o2 anion in the solid oxide crystal lattice.
Additional references of interest include the following.
B,C. LaRoy et al., in the Journal of the Electrochemical Society:
Electrochemical Science and Technolo~y, Vol . 120, No . 12 pp .
1668-1673, published in December 1973, disclose some electrical pro-perties of solid-state electrochemical oxygen sensors using vapor deposited thin films. Polycrystalline lanthanum fluoride solid 15 eiectrolytes were investigated at ambient temperature.
T, Horiba in U.S. Patent No. 4,550,067 discloses secondary cell batteries in which the positive electrode is made of materials such as phthalocyanine complexes, metal porphyrin complexes and the like.
Lyall in U,S. Patent No. 3,625,769 and Fouletier in U.S. Patent 20 No. 4,526,674 each disclose lithium/oxygen fuel cells.
Raleigh in U.S. Patent No. 4,118,194 and Weininger in U.S.
Patent No. 3,565,692, each disclose halogen electrochemical cells or the ITke .
Ledorenko in U,S, Patent NoO l~,172,022 and Eliot in U.S. Patent 25 No. 3,645,795, each disclose the use of phthalocyanine compounds in gas sensor electrodes.
~ . . ~
~3q:~75~
Zeitner in U.S. Patent NC). 3,909,297 discloses a lithium-chloride battery .
In U.S. Patent No. 3,698,955 and 3,719,564, Lilly discloses the use of rare earth fluorides such as lanthanum fluoride as solid 5 electrolytes which are deposited as their films in a battery and a gas sensor respectively.
~ :i.W. Mellors in European Patent Application No. 055,135 dis-closes a composition which can be used as a solid state electrolyte comprising at least 70 mole percent of ceriurn trifluoride and/or 10 lanthanum trifluorlde an alkaline earth metal compound e.g. fluoride, and an alalki metal compound e.g. Iithium fluoride.
Additional references cited also include the following, B.V. Tilak, R.5. Yeo, and S. Srinivasan tl981 j, "Electro-chemical Energy Conversion-Principles", in "Çomprehensive Treatise 15 of Electrochemistry" Vol. 3: Electrochemical Energy Conversion and Storage (J.O'M. Bockris et al. editors), pp. 39-122, Plenum Press, New York.
K.K. Ushiba, tl984), "Fuel Cells", Chemtech, vlay, pp. 300-307.
A. Sher, R. Solomon, K. Lee, and M.W, Muller ~1967), "Fluorine 20 Motion in LaF3", in "Lattice Defects and Their Interactions", R . R.
Hasiguti, Editor, pp. 363-405, Gordon and Breach Science Publishers, New York.
A. Yamaguchi and T. Matsuo (1981), "Fabrication of Room Tem-perature Oxygen Sensor Using Solid Electrolyte LaF3 (Japanese) ", 25 Keisoku-Jidoseigyo-Gakkai Ronbunshu, Vol 17(3), pp. 434-439.
M.A. Arnold and M.E, Meyerhoff (1984}, "lon-Selective Elec-trodes," Anal. Chem., Vol. 56, 20R-4BR.
. ~ , S. Kuwata, N. Miura, N. Yamazoe, anci T. Seiyama (1984), "Potentiometric Oxygen Sensor with Fluoride lon Conductors Operating at Lower-Temperatures ~Japanese)", J. Chem. Soc. Japan., 1984(8), pp. 1232-1236, and "Response of A Solid-State Potentiometric Sensor 5 Using LaF3 to A Small Amount of H2 or CO in Air at Lower Tempera-tures", Chemistry Letters, pp. 1295-129S, 1984.
M. Madou, S. Gaisford, and A. Sher (1986), "A Multifunctional Sensor for Humidity, Temperature, and Oxygen", Proc. of the 2nd International Meeting on Chemical Sensors, Bordeaux, France, pp.
10 376-379, A. McDougall ~1976), "Fuel Cells", Energy Alternatives Series (C,A. McAuliffe, series edltor), The Macmillan Press Ltd., London.
T. Takahashi (1984), "Fuel Cells (Japanese)", Chemistry One Point Series 8 (M. Taniguchi, èditor), Kyoritsu-shuppan, tokyo, lS Japan.
N. Yamazoe, N. ,J. tlisamoto, N. Miura, S, Kuwata (1968), "Solid State Oxygen Sensor Operative at Room Temperature", in Proc. of the 2nd Int. Meeting on Chemical Sensors, Bordeaux, France.
J, Meuldijk, J. and H.W. den Hartog (1983), "Charge Transport 20 in Sr~ LaxF2+x solid solutions. An lonic Thermocurrent Study", Physical Review B, 28(2), pp. 1036-1047.
H.W. den Hartog, K.F. Pen, and J. Meuldijk (1983), "Defect Structure and Charge Transport in Solid Solutions Ba1 xLaxF2+x", Physical Review B, 28(10), pp. 6031-601l0.
J. Schoonman, J., G. Overslui2en, and K.E.D. Wapenaar ~1980), "Solid Electrolyte Properties of LaF3", Solid State lonics, Vol. 1, pp.
211-221, , ' ' ~3~5i7~L
A.F. Aalders, A. Polman, A.F.M. Arts and H.W. de Wijn (1983~, "Fluorine Mobitity in i al_xBaxF3_x (O~x~0.1) Studied by Nuclear Magnetic Resonance", Solid State lonics, Vol. 9 ~ 10, pp. 539-5~2.
A. K . Ivanovshits, N . I . Sorokin, P. P. Fedorov, and B . P.
S Sobolev ~1983~, "Conductivlty of Sr1_xBa~F3_x Solld Solutiorls wit ompositions in the Range 0.03sxsO.40, "Sov. Phys. Solid State, 25(6), pp. 1007-lOtO.
J. O'M. Bockrls, and T. Otawaga (1984), "The Electrocatalysis of Oxygen Evolutlon on Perovskltesl', J. Electrochemical. Soc., 10 t31 ~2), pp. 290-302, Adciltional general inforrr;aeion is found in "Fuel Cells" by E,~.
Calrns et al. in ~ r~
13rd Ed.), Vol. 3, pp. 54S-568; and in "Fuel Cells" by O.J. Adlhart in a~ , 6th ed., D.M. Considine 15 Iedl, Van Nostrand Reinhold Co., New York, pp. 1296-1299, 1986.
Solid electroiyte fuel cells have .several advantages over the other types of fuel cells:
1. There are no litluids involved and, hence, the problems 20 associtated wlth pore flooding, maintenance of a stable three-phase interface, and corroslon are totally avoided.
SOLID COMPOSITIONS FC)R
FUEI CELLS SENSORS AND CATALYSTS
. _____ BACKGROUND OF THE INVENTION
Fi~ d ~f the In~n~ G~
The present invention relates ~:o materlals and processes to prepare polycrystal and monocrystal forms for use in fuel cells in sensors and as catalys~s. In specific embodiments, a fuel cell having oxygenlsolid lanthanum fluoride (as a single crystal)/hydrogen configuration produces about 1 volt of open circuit potential at 10 essentially ambient temperature. In other speciflc embodiments, specific mixed lanthanide or alkaline earth fluorides also produce electricity at moderate: temperatures. Embodiments also include a porous perovskite-type metallic transition metal oxide electrode and a lanthanum metailalkaline earth/fluoride elec~rolyte which are useful as 15 a soild electrode/electrolyte in a fuel cell, as a sensor, or as a catalyst .
DES:CRIPTII:)N OF THE RELEVANT ART
Fuel cells convert chemical energy :to electrical energy directly, without ~ having a Carnot-cycle effic~ency limitat~on, through 20 electrochemica! oxidation-reduct10n reactions of fuels. Several types of fuel cells have been or are being investigated at the present time.
;
, ~ ~,J
. . ,, ~, . .
The solid electrolyte fuel cell which can be considered as the third generation fuel cell technology, i~ essentially an oxygen-hydrogen (or H2-C0 mixture~ fuel cell operated at high temperature lca. 1000C) ~ith a solid ceramic oxide material used as S the electrolyte. At present, yttrium- or calcium-stabilked zirconium oxides have been used as the electrolyte. The mechanism of ionic conduction is oxygen ion transport via o2 anion in the solid oxide crystal lattice.
Additional references of interest include the following.
B,C. LaRoy et al., in the Journal of the Electrochemical Society:
Electrochemical Science and Technolo~y, Vol . 120, No . 12 pp .
1668-1673, published in December 1973, disclose some electrical pro-perties of solid-state electrochemical oxygen sensors using vapor deposited thin films. Polycrystalline lanthanum fluoride solid 15 eiectrolytes were investigated at ambient temperature.
T, Horiba in U.S. Patent No. 4,550,067 discloses secondary cell batteries in which the positive electrode is made of materials such as phthalocyanine complexes, metal porphyrin complexes and the like.
Lyall in U,S. Patent No. 3,625,769 and Fouletier in U.S. Patent 20 No. 4,526,674 each disclose lithium/oxygen fuel cells.
Raleigh in U.S. Patent No. 4,118,194 and Weininger in U.S.
Patent No. 3,565,692, each disclose halogen electrochemical cells or the ITke .
Ledorenko in U,S, Patent NoO l~,172,022 and Eliot in U.S. Patent 25 No. 3,645,795, each disclose the use of phthalocyanine compounds in gas sensor electrodes.
~ . . ~
~3q:~75~
Zeitner in U.S. Patent NC). 3,909,297 discloses a lithium-chloride battery .
In U.S. Patent No. 3,698,955 and 3,719,564, Lilly discloses the use of rare earth fluorides such as lanthanum fluoride as solid 5 electrolytes which are deposited as their films in a battery and a gas sensor respectively.
~ :i.W. Mellors in European Patent Application No. 055,135 dis-closes a composition which can be used as a solid state electrolyte comprising at least 70 mole percent of ceriurn trifluoride and/or 10 lanthanum trifluorlde an alkaline earth metal compound e.g. fluoride, and an alalki metal compound e.g. Iithium fluoride.
Additional references cited also include the following, B.V. Tilak, R.5. Yeo, and S. Srinivasan tl981 j, "Electro-chemical Energy Conversion-Principles", in "Çomprehensive Treatise 15 of Electrochemistry" Vol. 3: Electrochemical Energy Conversion and Storage (J.O'M. Bockris et al. editors), pp. 39-122, Plenum Press, New York.
K.K. Ushiba, tl984), "Fuel Cells", Chemtech, vlay, pp. 300-307.
A. Sher, R. Solomon, K. Lee, and M.W, Muller ~1967), "Fluorine 20 Motion in LaF3", in "Lattice Defects and Their Interactions", R . R.
Hasiguti, Editor, pp. 363-405, Gordon and Breach Science Publishers, New York.
A. Yamaguchi and T. Matsuo (1981), "Fabrication of Room Tem-perature Oxygen Sensor Using Solid Electrolyte LaF3 (Japanese) ", 25 Keisoku-Jidoseigyo-Gakkai Ronbunshu, Vol 17(3), pp. 434-439.
M.A. Arnold and M.E, Meyerhoff (1984}, "lon-Selective Elec-trodes," Anal. Chem., Vol. 56, 20R-4BR.
. ~ , S. Kuwata, N. Miura, N. Yamazoe, anci T. Seiyama (1984), "Potentiometric Oxygen Sensor with Fluoride lon Conductors Operating at Lower-Temperatures ~Japanese)", J. Chem. Soc. Japan., 1984(8), pp. 1232-1236, and "Response of A Solid-State Potentiometric Sensor 5 Using LaF3 to A Small Amount of H2 or CO in Air at Lower Tempera-tures", Chemistry Letters, pp. 1295-129S, 1984.
M. Madou, S. Gaisford, and A. Sher (1986), "A Multifunctional Sensor for Humidity, Temperature, and Oxygen", Proc. of the 2nd International Meeting on Chemical Sensors, Bordeaux, France, pp.
10 376-379, A. McDougall ~1976), "Fuel Cells", Energy Alternatives Series (C,A. McAuliffe, series edltor), The Macmillan Press Ltd., London.
T. Takahashi (1984), "Fuel Cells (Japanese)", Chemistry One Point Series 8 (M. Taniguchi, èditor), Kyoritsu-shuppan, tokyo, lS Japan.
N. Yamazoe, N. ,J. tlisamoto, N. Miura, S, Kuwata (1968), "Solid State Oxygen Sensor Operative at Room Temperature", in Proc. of the 2nd Int. Meeting on Chemical Sensors, Bordeaux, France.
J, Meuldijk, J. and H.W. den Hartog (1983), "Charge Transport 20 in Sr~ LaxF2+x solid solutions. An lonic Thermocurrent Study", Physical Review B, 28(2), pp. 1036-1047.
H.W. den Hartog, K.F. Pen, and J. Meuldijk (1983), "Defect Structure and Charge Transport in Solid Solutions Ba1 xLaxF2+x", Physical Review B, 28(10), pp. 6031-601l0.
J. Schoonman, J., G. Overslui2en, and K.E.D. Wapenaar ~1980), "Solid Electrolyte Properties of LaF3", Solid State lonics, Vol. 1, pp.
211-221, , ' ' ~3~5i7~L
A.F. Aalders, A. Polman, A.F.M. Arts and H.W. de Wijn (1983~, "Fluorine Mobitity in i al_xBaxF3_x (O~x~0.1) Studied by Nuclear Magnetic Resonance", Solid State lonics, Vol. 9 ~ 10, pp. 539-5~2.
A. K . Ivanovshits, N . I . Sorokin, P. P. Fedorov, and B . P.
S Sobolev ~1983~, "Conductivlty of Sr1_xBa~F3_x Solld Solutiorls wit ompositions in the Range 0.03sxsO.40, "Sov. Phys. Solid State, 25(6), pp. 1007-lOtO.
J. O'M. Bockrls, and T. Otawaga (1984), "The Electrocatalysis of Oxygen Evolutlon on Perovskltesl', J. Electrochemical. Soc., 10 t31 ~2), pp. 290-302, Adciltional general inforrr;aeion is found in "Fuel Cells" by E,~.
Calrns et al. in ~ r~
13rd Ed.), Vol. 3, pp. 54S-568; and in "Fuel Cells" by O.J. Adlhart in a~ , 6th ed., D.M. Considine 15 Iedl, Van Nostrand Reinhold Co., New York, pp. 1296-1299, 1986.
Solid electroiyte fuel cells have .several advantages over the other types of fuel cells:
1. There are no litluids involved and, hence, the problems 20 associtated wlth pore flooding, maintenance of a stable three-phase interface, and corroslon are totally avoided.
2. Being a pure solid-state cievice, It poses ~irtually no main-tenance problems. For example, the electrolyte compas~t~on i5 invari-ant and Independent of the compositlon of the fuet and oxidant 25 streams,
3, inexp n~ive metallic oxides tceramics) rather than expensive platinum can be used as the electrode catalysts.
",, .", ~ :., . ~
- ~3~57~
ll. The solid electrolyte fuel celis demand less ~eed gas prepa-ration than the phosphoric aeid cell, which requires a converslon of CQ to H2 via the wa~r-gas shift rear~ion, or the molten carbonate cell, which require~ a carbon dioxide 5 loop due to the use of carbonate ions for ionic transport.
The attraction of developing a ~olid eleetrolyte fuel ceil is its simplicity. However, a high operation ~emperature (ca. tO00C) is by far the most criticat aspec~ of this ~ype of fuel cell. Although high operation temperature produces high-quality exhaust heat that can 10 ~enerate additional electrical power, leading to a hlgh overall system efficiency, maingainlng the integrity of the cell components such as the interconnector is the most difficult challenge.
It is therefore desirable to develop alternative low temperature solid materials and composites for use as solid electrolytes in fuel 15 cells, as solid sensors and as solid catalysts that can be operated in a range of 400~600C or lower (preferably about 200C, especially at ambient temperature]. Some ~f ~he structures described herein have been examined for usefulness as battery electrolytes. However, none of the references cited hereinabove, individually or collectively, 20 disclose or suggest the present invention as deseribed herein. The present invention relates to the design of such low temperature solid electrolyte fuei cells, sensors, or catalysts based on non-oxide solid electroly~es, such as solid solutiorls of lanthanide fluorides (e.g.
LaX~rl-XF2-~XI-. , . . .
,, ~ . . . .
~3iQ)~7~
SUMMARY OF THi INVENTION
The present invention relates to soiid materials which have application as an electrolyte for a fuel ceil, a sensor or a catalyst.
More specifically, the present invention relates to a solid material 5 IAA] for use as an electrolyte for a fuel cell or for a sensor or as a catalyst, each ha~ing a polycrystal or single crystal s~ructure, com-prising:
~a1 a structure of the formula:
10 wherein A is independently selected from lanthanum, cerium, neo-dynium, praseodynium, scandium or mixtures thereof, wherein AF3 is a single crystal or a portion thereof, (b) a structure of the formula:
Pbl _XMX F2_X
15 wnerein M is independently s~lected from potassium, or silver, and x is between about 0 . 0001 and 0 . 25, (c) a structure of the formuia:
Pbl -x B ix F2+x wherein x is defined herein above;
(d) a structure of the formula:
AyBl _yF2+y wherein:
A as defined hereinabove, B is independently selected from strontium, calcium, barium or 25 magnesium, and y is between about 0.0001 and 1 (e) a structure of the formula:
AyBl -y-zLiF2+y+z ~3~5~
wherein A, B and y are as definad hereinabove, ~ is between about 0. 0001 and 0.10 wherein y l ~ is less than or eq~al to 1;
(f) a structure of the formula:
N1 _n_~l~UnCerl~F2~2n+m 5 wherein N is independently selected from calcium, strontium or bar-ium, n is between about 0. 0001 and 0. 05, and m is between about 0 . 0001 and 0 . 35;
tg) a structure of the formula:
PbSn F4 10 with the proviso that PbSnF4 is only useful as a fuel cell electrolyte;
th~ a structure of the formula:
KSn2F5;
(i) a structure of the formula: , ~' Srcl2-K
tj) a structure of the formula:
:
Laol _pF1 +2p wherein p is between about 0.0001 and 0.9999;
~` tk) a structure of the formula:
PbSnFq PhSnOr 20 wherein q and r are each independently from between about 0 . 0001 and 1;
(I) a structure of the formula:
tAOl~5)ytGF2}l_y : wherein A is as defined hereinabove, y is between about 0.0001 and : 25 1, and G is independently selectecl from calcium and magnesium; and (m) a structure of the formula:
~, SmaNdbFcOd ~:' . ... .
~3~;75~
wherein a and b are each independently between about 2.18 and 9.82 and c i5 between about 12 and 29. 45, and d is between about 3 . 25 and 12, with the proviso that a~b is about 12 and c+2d is about 36.
In another aspect, the present invention relates to a process for 5 the preparation of an electrolyte for a fuel cell or for a sensor, which process comprises:
(a) reacting a structure of material [AA] above in an atmosphere comprising a mixture of oxygen and wa~er wherein the water is present in between about 1 and 9996 by weight at between 100 lO and 1000C for between about 10 and 50 hrs.
In another aspect, the present invention relates to a process for the preparation of an electrolyte for a fuei cell or for a sensor, which process comprises: .
(a) subiecting, for instance, about one gram of a structure of lS material [AA] above to a current of about 10 3 amperes per square centimeter at a temperature of between 0 and 400C for a time sufficient to transmit a certain amount of coulombs equivalent to a product of one Faraday (coulombs/mole) times X where X is between about 0 . 001 and 1, depending upon the specific material structure.
In another aspect, the present invention relates to a process ~BB] for preparing a composite consisting essentially o~:
1-y y 3 having a perovskite or a perovskite-type structure as an electrode catalyst in combination with:
2 5 y 1 ~y 2+y s~
- 1 o -as a discontinuous surface coating solid electrolyte wherein A is independently selected from lanthanum, cerium, neodymium, praseo-dymium, or scandium, B is independently selected from strontium, calcium, barium or magnesium, Q is indepenciently selected from 5 nickel, cobalt, iron or manganese, and y is between about 0. 0001 and 1, which process comprises:
~a~ obtaining a particulate of:
l-y y 3 wherein A, B and y are defined hereinabove having an average lO crystal size distribution of between about 50 and 200 Angstroms in dTameter and a surface area of between about 10 and 100 meters 2/grams and formed into a film-like or pellet-like shape having a general thickness of between about 1 ancl 5mm, a pore size of between about 25 and 200 Anstrorns and (b~ reacting the particlulate of step (a) with a vapor comprisi ng:
Ay B 1 -y F2~y wherein A, B and y are defined hereinabove, at about ambient pres-sure at between about 0 and 1000C: for between about 10 and 30 hr.
20 obtain the composite of between about 25 to 1000 microns in ~hickness; and (c) recovering the composite of step (b) having muttiple inter-faces between:
A1_yByQO3 and AyB1 yF2+
25 said composite having a pore size of between about 25 and 200 Angstroms and a surface area of between about 10 and I 00 meters Igram .
.
,, ~5~5~
A preferred embodîment in this process ~BB] is wherein A is lanthanum, B strontium, Q is cobalt, and especially where y is about 0~3. Another preferred embodiment of process ~E3B] is wherein A is selected from cerium or scandium, B is selected from strontium or 5 magnesium, Q is selected from nickel, cobalt or manganese and y is between about 0. 2 and 0. 4.
In another aspect the present invention relates to the use of the composite of Claim 16 selected from electrodelelectrolyte for a fuel cell, a sensor, or a contact catalyst for synthesis or degradation.
The use of the composite material of Claim 28 as an elec-trode/electrolyte for a fuel cell or a sensor.
The use of the composite material of Claim 30 as an oxygen sensor or a fuel cel 1.
In another aspect the present invention relates to the process lS for the generation of electricity, which process comprises:
~ a) contacting a solid electrolyte of EAA] above or :prepared by process [BB] above with a fuel at between about 0 and 1000C.
In another aspect the present invention relates to the process described herein wherein the fuel ~or the fuel cell is setected from 20 hydrogen, hydrazine, ammonia, fossil fuels, separate components of fossil fuels, or mixtures thereof, wherein all fuels have a boiling point at ambient temperature of 25~C or less. It is especially useful to obtain a fuel cel I having an operating temperature between about lû and 30C.
In another aspect, the composite material may be prepared by replacin~ the perovskite-type structure of the process [BB] with a ~ .
metal phthalocyanine structure, wherein the metal is selected from iron, cobalt, nickel and the like.
In still another aspect, the perovskite-type electrode (or the metal-phthalocyanine elecl:rode) and the discontinuous fluoride 5 electrolyte of process [BB] are each thin films of between about 1 and 25 microns on a conventional inorganic catalyst support~
BRIEF_DESCRIPTION OF THE DRAWINGS
Figure 1 shows Table 1 as a comparison of varlous types of fuel cel Is .
Figure 2 shows the open clrcuit voltage (VOC) versus time using a slngle crystal of lanthanum fluorlde (LaF3).
Flgure 3 shows a configuration of a fuel cell using, for instance, a single crystal of thinly^machined and poltshed lan~hanium fiuoride.
Figure 4 shows a curve of the open circuit voltage versus time 15 using a single crystal of lanthanum fluoridP (LaF3). Figure 4 is at 0.575 volts using Pd/Pt electrodes.
Figure 5 is a table showing the open circuit voltage tVOc) for alr, nitrogen, oxygen and hydrogen.
Figure 6 is a cross section of a solid material composite for solid 0 electrode/electrolyte having a Pt contact, a sslid coating of an 9 0.7Sr0.3F2.7 with a perovskite-type electrod ( LaO 75rO,3CoO3)~
Figure 6A is an enlarged cross section showing the discontinuous nature of the electrolyte on a pore opening of the porous electrocle.
Figure 7 is a cross section of a solid material composite useful as a solid electrode having a catalyst support, a platinum contact, a solid coating of an electrolyte (e.g., La 75r0 3F2 7) with a solid 7Si~
discontinuous coating of a perovskite-type te.g., LaO 75r0 3CoO3) or a metal phthalocyanine (Co,Ni, or Fe phthalocyanine~ electrode.
Figure 7A is an enlarged cross section showing the discontinuous nature of the electrolyte in contact with the ele~trode on the soiid 5 support.
DETAILED DESCRIPTION OF TIIE
In the present invention, lanthanum fluoride is the solid elec-trolyte of choice for a fuel cell, or a sensor. Its properties are 10 shown below in Table 2, Table 2 PRO PERT I ES OF LaF
Crystal structure: hexagonal space group is P63/mcm -D36h -with twelve formula units per cell, -Melting Point: 1493C, -Density: 5, 936, -Dielectric constant: 14 (at 10MHz), -Thermal conductivity: 0.025 (W cm 1deg 1), -Electrical conductivity ~ 10 7 Q 1cm-1 (at 25C) -Transmits light from the vacuum ultraviolet into the infrared, -The effective Debye temperature is.~360K, -The activation energy for fluorine ion diffusion is ~0 . 45 eV, -Activation energy for the formation of defects: -0 . 07eV, -Birefringence: ~n=0.006, -Thermal expansion coefficient: 11x10 ~ cmicm/C ~c-axis, 25C), a good match is Cu, ' ~3~7~
LaF3 has unique physicochemical properties such as high elec-trical conductivity and high polarizability at room temperature. The Debye temperature of LaF3 is only 360K, while its melting point is as high as 1 766K . The observed phenomena appear to be associated S with the formation of Schottky defects and with the diffusion of defects has the unusual Iy low value of ~0 . 07 eV, and the room tem-perature Schottky defect density is about 101 9/cm3 .
Fluorine in LaF3 usually exists in three magnetically nom-equivalent sites. Covalent bonding predominates in two of the sites.
10 In the third slte, the fluorines make up a layered array with approxi-mately 60% ionic bonding and about 4~ 1r-bonding. The high po-larizability and high conductivity of LaF3 at room temperature is primarily due to the motion of F ions through the latter sites. The relatively small radius of F is almost identical with that of the oxide 15 o2 ion (1.25 A); therefore oxide ions (o2 ions) can substitute for the F ions in LaF3. It has been confirmed the oxycien ion transport through the bulk of a single crystal LaF3 by Auger electron spectroscopy. In other words, the solid electrolyte Lai~3 serves as a supporting eiectrolyte analogous to liquid phase in which oxygen ions 20 can move freely.
Lanthanum Fluoride as a Soiid Electrolyte for F_! Cell :
Traditionaily LaF3 has been extensiv21y used as a F ion selec-tive electrode in electroanalytical chemistry. Recently LaF3 has been applied to a room temperature potentiometric oxygen sensor and to a 25 multifunctional sensor; for humidity, temperature, oxygen gas, and dissolved oxygen. However, no disclosure exists concerning the use of LaF3 material dS a single crystal as a solid electrolyte In a fuel 5~5~
cell. In earlier investigations, it was determined that polycrystalline lanthanum fluoride as a thin film solid electrocle was unreliable and unpredictable. About one of ten electrodes prepared shorted out under laboratory conditions. As is described below, the singie 5 crystal lanthanum fluoricle solid electrolyte was reliable and predictable .
Figure 2 illustrates a result on a LaF3 fuel cell. In this case, a single crystal of between absut 10 and 100 mils is used. As shown in Figure 3, one cm diameter single crystal LaF3 with a thickness of 25 l0 mils was used. A comb-shape noble metal (Pt, Au, or Pd) electrode (21 + 21A) was sputtered on both sides of the LaF3 sample 22. One electrode was exposed to pure hydrogen and the other was exposed to room air. A Pt/Pt system exhibited an open circuTt potential (VOC) of about 0 . 6 volts at room temperature . The result was repeatabla upon 15 on an on/off cycle of hydrogen. When the Pt/oxygen cathode 21 was replaced by a Pd electrode with a different configuratlon, VOC was increased to 0. 88 volts. However, in either case, the observed short circuit currents were in the order of 10 3 Amperes. This small amount of current is due to the fact that, in the electrode 20 configuration used in our experiments, the total area of the triple-interface ~i.e. gas, electrode catalyst, and solid electrolyte) available for electrochemical reactions was extremely small. Current density is greatly increased when a large surface area platinum black is used as an electrode.
The following electrochemical reactions rnay take place at each electrode:
Cathode: 2 + 4e = 20, Anode: 2H2 + 202 - 2H20 + 4e 5 Effect on VOc of Oxygen Partial Pressure Differences Between Working and Counter Electrodes A study was made to determine how a difference in oxygen partial pressures on either side of the solid electrolyte contributed to the measured VOc values. The relation used was 10 VOc = RT/4F In P0 (At electrode #1 ) / P0 tAt electrode #2) where P0 stands for partial pressure of oxygen at the electrode specified, R is the universal gas constant, T Is the temperature in Kelvln, and ; F is Faraday's constant.
However, from the results seen in Fi~ure 4 and in Figure 5 15 tTable 3) the oxygen partial pressure differences do not determine :: .
the measured VOc with air at working electrode and oxygen at the counter electrode. This will confirm the result that the observed VOc - ~ is indeed due to a fuel ce!l function.
Those solid materials containing both lanthanurn and fluorine 20 ~especially structure of formula ta) ), are very attractive as solid electrolytes in low temperatures (10 to 30QC) solid eiectrolyte of fuel cel Is .
In preferred embodlments of material iAA~ above, each of the structures (a) through tm) are each independently preferred as a 25 solid electrolyte for a fuel cell, a solid electrolyte for a sensor or as a catalyst, espeacially as fuel cell or a sensor.
, ~L3~S~
ln a preferred embodiment, the solid material material lAA] of the SUMMARY is selected from structures of formula ~a), (b), (d~, (e) or (j). In another embodiment the solid material of [AA] of the SUMMARY is selected from structures of formula (a), ~b), (f), (h), 5 (j) or (k).
Other preferred embodiments of the solid material include the foi lowing:
[1 l fuel cell of material [AA] above has a useful operational temperature range of between about 0 and 1 000C especially wherein l0 the structure in subpart (a) is AF3 wherein A is lanthanum, and also where the operational temperature Is between about 15 and 30C;
[2] the electrolyte of material [AA] is used in a device as a sensor to detect gases selected from oxygen in the gaseous phase or dissolved in a liquid;
15l3] the electrolyte of material [AA] is used for a sensor wherein the sensor has a useful operating range of between about -40C to + 1000C or [4~ the solid material IAA] above as an electrolyte for a sensor of [AA] above is wherein the oxygen sensor has an operating range 20 of between about 0C and 600C.
In the present invention the solid materials of [AA] are unless otherwise stipulated, individually preferred as a component of a fuel cel I, of a sensor or as a catalyst useful In the interconversion formation and degradation of organlc compounds, nltrogen-containing 25 compouncls and the like.
It is intended that the soli~ materials described herein for use as solld electrolytes for fuel and for sensors optlonally include '~L3Qt3 pretreatment of the surfac& of the solid, preferably structures of formula (a), especially where A is lanthanum as described herein below .
Pretreatment U_~ Oxygen Atmosphere An instrinsic single crystal of LaF3 has a conductivity of 10 7 ohm 1 cm 1 (which is mainly due to F lons) at room temperature. It Is suggested that the oxygen ion conductivity in I aF3 may be in-creased simply by sintering the crystal in an oxygen gas atmosphere because some of F ions may be replaced by o2 ions. Recently, - 10 Yamazoe et al., tsupra) r~ported that the response time of LaF3 oxygen sensor was dramatically improved by the treatment of LaF3 in a stream of air containing 15 torr of water vapor at 1 50C for 12 hr .
This Improvement is presumably due to the formation of a lanthanum oxy fluoride at the surface (the chemical composition may be written - 15 as lanthanum oxyfluoride of the structure [j~ in material lAA] above.
In the present invention, the materials describ~d in the Summary of the Invention (and in S:laim 1 ) are sintered in an oxygen environ-ment at elevated temperature. The material is placed in an oxygen atmosph~re containing from 1 to 99 percent by weight of water.
20 Usually the water present is between about 10 and 30 percent by weight especially about 15 percent by weight. The temperature is usually between about 100 and 1000C, preferably between about 150 and 600C, especially between about 200 and 400C.
It is also possible to pretreat a ~olld material IAA] to enhance its lonic conductivity by contacting the material with a polarizing electrical current. Thus, the electrochemical doping (pumping) of .
;;7~i1 , g oxide ions is achieved by subjecting about 1 gram the material [AA]
to 10 3 amperes per square centimeter for between about 1 to 25 hr at ambient temperature. Stated in another way about 1 gram of the structure of the material [AAl above is subjected to a certain amount 5 of coulombs equivalent to a product of one Faraday (coulombs/mole) times X where X is be~ween about 0. 001 and t a depending on the specific material [AA] structure (a) to (m~. This electrochemical pumping may be performed between about O and 400C.
An E!ectrodelElect o y~te 10 Perovskite-type In general, the electrocatalysts for the above cited low tempera-ture solid electrolyte fuel cell can be noble metals ~e.g. platinum), their alloys or blacks, metal-phthalocyanines, transition metal cata-Iysts (e.g. Ni/NiO), and metallic transition metal oxides (e.g.
15 LaO gSrO lMnO3)0 Particularly, it is of interest to use electronically conductive perovsklte-type oxide: e.g.:
A1 -x Bx Q3 where A, B, Q and x are as defined hereinabove as catalytic 20 electrode materials, especially for the oxygen reaction in conjunction with the tanthanlde fluoride solid electrolyte:
:
- Ax B 1 -x F2+x wherein A is: (La, Ce, Nd, Pr or Sc);
and E3 is: (Sr, Ca, Ba or Mg);
25 and x is between about 0.00l and 1.
An example of such a composite electrode/electrolyte system would be: LaO 75rO 3C03lLao.7sro~3F2~7-- : .
' .
~5~
On this interface the electronically conductive phase (electrode: La~ 75r0 3F~ 7) exist adjaoently to aach other and even may be mixed on an atomic-level by sharing La and Sr atoms.
In designing systems of A1_XBxQ3/AxE~1-xF2~x~
one can choose atoms for A and B in such a way that there is a maximum degree of matching in ~he lattice parame~ers ~nd thermal coefficients of the two phases. Therefore, the composite system A1 _XBx~:)O3lAxBl-xF2~x 10 can be an Ideal site to facilitate the following reaction:
2 + 4e = 2O2, beeause a well defined, stable atomic scale three-phase inter~ace (gas, electrode, electrolyte) can be established in the Al xBxQo3/Axi3~-xF2 tX
The perovskites useful in this invention may be purchased or may fe formed according to the procedures described in the literature e . g ., T . Kudo et ai ., U . S, Patent No. 3, 804, 674 .
A typical perovskite preparation is described below in Example 20 ~-Figure 6 shows the confis3uration of a composite for use in a fuel cell. The perovsklte substrate (porbus oxide) electrode 61 jc treated with a vapor to deposit the fiuoride electrolyte 62 on the surface. As shown in Figure 6A fluoride 62 or 65 will enter the pores of the 25 perovskite and also be on the surface 64 of the perovskite in a discontin(Jous manner. In thi~ way, millions of two material catalytic , ,~
57~.
surfaces sites 66 are created to factlitate the electrochemical reaction at the intersection of the perovskite 61 and fluoride (62 or 65).
Figure 7 shows the configuration of a supported composite for use in a fuel cell. The perovsklte substrate 7t is spray dried onto 5 an inor~anic support 7û such as silica ~horia zirconia magnesia or the like having mechanical stability. The fluoride electralyte 72 is then vapor deposited on the surface of the perovskite 71. As shown in Figure 7A the fluoride electrolyte 72 as a vapor enters the pores of the perovsklte ~1 and the substrate 70 in a discontinuous manner.
lO In this way millions of two-material catalytic surfaces 74 are created to facilltate the eiectrochemical reaction at the intersection of the perovskite 71 and fluoride 72.
~;n~
The present invention also contemplates the use of 15 metal-phthalocyanines in electrode/electrolyte composites. In this embodiment of the invention the metal-phthalocyanine (~-phthalocyanine~ is used to replace the perovskite-type oxide described above on a weight to weight basis and is then combined with the solid electroiyte as is described above. The metal ions (Z-) 20 preferred include iron cobalt nickel and the like.
Typical metal-phthalocyanines in these composites include those described above and for example those and similar ones described by K.V. Kordesch in U~S. Patent No. 3 783 026.
The composites described below in Claims 28 2g~ 30 or 31 arP
preferred .
. , .
. ,~ ; ~.
~3~7S~`
Sensors The use of the structures disclosed herein are described sensors in analiytical devices to determine components in the vapor phase and also in the liquid phase.
These sensors are preferably useful to analyze oxygen, carbon dioxide, methane, ethane, ethylene, ammonia, hydrogen sulfide or the Iike. Lanthanum fluoride is preferred to analyze oxygen in a gaseous phase or in a liquid, preferably an aqueous solution.
The range of the analysis may be from between about a part per 10 billion to lO,000 parts per million in the gas phase tusually performed in the potentiometric mode~. Even high concentratlons of a component, for instance, in the liquid phase determined in the current mode i3ecause the proportionality is linear rather than logrithmic.
For the structures defined above in the summary in a preferred embodiment the solid material for use as an electrolyte in a fuel cell or in a sensor or for use as catalyst is selected from structures of (b), (c), (d), (e), ~f), th), (i), (j), (k), ~I), or (m). A more preferred embodiment of the solid material is selected from the 20 structures of (b~ i (C), (d), or (e) . Another preferred embodiment of the solid material is selected from the structures of (k), (I) or (m).
The following Examples are intended to be illustrative only and ;~ are not to be construed as limiting in any way.
:: :
,:
Formation of Solid Th;n Films and Fuel (:ell Measurements ~aa) As is described in B.C. LaRoy et al., above, lead 75 potassium 25 fluoride 5 . 75 (Pbo 75Ko 25F1 75) is evaporated onto in a thin polycrystalline f71m onto a substrate to a thickness of 25 mils. Pt black Is coated onto the polycrystalline film. One electrode is exposed to pure hydrogen and the other is exposed to room alr. This Ptlsotid etectrode/Pt system is expected to exhibit a useful open circuit, l0 potential (VOc~ of between about 0.5 and 1.0 volts.
(bb) The procedure of subpart laa~ above is repeated, except that the Pbo 75K~ ~5F1 75 is replaced by an equivalent weight of P~.75~3~.25F1 .75~
(cc~ The procedure of subpart (aa) above is repeated, except e Pbo.~5Ko.25Fl,75 is repla ed by an equivalent weight of La,3Sr.7i 2.3~
(dd) The proeedure of subpart (aa) above is repeated, except that the Pbo 75Ko 25F1 75 is replaced by an equivalent weight of LaO 4Sr 5LiF2 5~
~o : (ee) The procedure of subpart (aa) above is: repeated, except e Pboo75Ko,25F1,75 is replaced by an equivalent weight of :
.88U,~2Ce,1F2,~4~ :
(ff) The procedure of subpart (aa) above is repeated, except that the Pbo 75Ko 25F1 75 is replaced by an equivaient weight of 25 PbSnF~
~, ....
' ,~.,~
,~.., ,. ,::, ~3~
(gg) The procedure of subpart (aa) above is repeated, except that the Pbo 7sKo 25F1 75 is replaced by an equivalent weight of KSnF5.
thh) The procedure of subpart taa) above is repeated, except 5 that the Pbo 7sKo 2sF1 75 iS replaced by an equivalent weight of SrC12- KCI.
(ii) The procedure of subpart ~aa) above is repeated, except t e Pbo.75Ko.25Fl.75 is replaced by an equivalent weight of LaO, 7Y Fl, 6 -(jj) The procedure of subpart (aa) above is repeated, except t the Pbo,75Ko.25FI,75 is replaced by an equivalent weight of PbSnF0 3 ~ PbSnOo . 4-~ (kk) The procedure of subpart (aa) above is repeated, except ; the Pbo.75Ko.25Fj.75 is replaced by an equivalent weight of 15 (LaO1 5)0.S~caF2)o-5-(Il) The procedure of subpart (aa) above is repeated, except the Pbo.75Ko.25Fl.75 is replaced by an equivalent weight of Sm6Nd6F1 89 .
In subparts ~bb) to (Il) the fuel cell obtained is expected to 20 generate a useful open circuit potential tVOc) of between about 0.5 and 1 . 0 voits . ~ ~
EXAhiPLE 2 FORI~AATION OF A PEROVSKITE FOR AN ELECTi~ODE
.
A pure lanthanum nickelate crystal Is synthesized by a 25 co-precipitation technique. The starting materials are LatNO3)3-6H2O
and NitNO3~2 6H2O talternatively acetates and chlorides can be used as the starting materials ) . The proper amounts of each nitrate 5~L
required to give ~he desired stoichiome~ry are weighed and dissolved In doubly disttiled water to remove Na+ and separated quickly by a centrlfuge teGhnique at 2000 rpm for 'i5 min., since Ni(OH)2 tends to dlssolve at pH-7. Thls procPss is repe,ateci several times. The 5 obtained precipitates are dried in an oven at 1 00C overnight. The dried powder is ~hen put in the furnace at 800C for 16 hours in an 2 atmosphere. The electrode is made by pressing the powders into 13mm diameter pellet (Beckman model K-13 die) at a pressure of 300kg cm 2, The pellet is sintered a~ 750C in an 2 atmosphere for 48 q hours and the perovskite pellet is recovered.
A thin film tabout 100 mlcrometers) of LaO 5SrO 5F2 5 iS
prepared on the perovskite layer by conventional vacuum evaporation (LeRoy et al. ) using pure materia~s of lanthanum fluoride and strontium fluoride in a tungsten boat applying a current of about 40 15 amperes in a high vacuum of abous 10 torr. The composite obtained is expected to have a useful open ircuit potential of between about 0. 5 and 1 . 0 volts .
A Porous Substrate-LaO 5SrO.5coo3 ~film) LaO,5S o,5 2.5 20 bv S~raY Pvrolvsis/Vacuum Evaporation or Reactive S~utterina , _~
taa) A thin layer of a perovskite oxide is prepared on a porous substrate 5e.g. alumina, zirronia oxide with pore size of abut 100 A
with a ~hickness 1-2 mm) by a spray pyrolysis. As an exampie, the 50~ Sr doped LaCoO3 is prepared as follows: 8.5g Sr(NO3)2, 23.39 25 Co(NO3)2-~H2O and 17.81g La(iNO3~3~6H2O (alternatively acetates and chiorldes can be used as the starting materials) ara dissolved in dlsltllled wat~r and sprayed onto the hot porous substrate ~about 10 * l~rade-mark , I ", !
cm by 10 cm) at a flow rate of about 10 mL/min. The homogeneous constituent is then decomposed at 250C, followed by quenching oxygen and heating 500C, in air for 3hr. The perovskite catalyst loadin~ should be about 10mg/cm2. Then, a thin film ~about 100~1m) 5 of LaO 5SrO 5F2 5 is prepared on the perovskite layer by a vacuum evaporatlon using pure materials of LaF3 and SrF2 in a tungsten boat and applying a current of about 40 Amperes in high vacuum of about t0 7 torr. Alternatively pure metal targets can be used in a sputtering process in a low pressure fluorine atmosphere (e.g. 10 m l0 torr). The obtained fuel cell is expected to generate an open circuit potential (VOC) of between about 0 . 5 and 1 . 0 volts . tSee Figure 6, 6A, 7, 7A ) .
In the above (aa) subpart the reaction i5 repeated using an equivalent weight of nickel phthalocyanine for the perovskite. The 15 composite formed is expected to have a useful open circult potential of between about 0. 5 and 1 . 0 volts .
:
: FORMATION OF A SINGLE CRYSTAL BASED FUEL CELL
A single crystal of lanthanum fluorlde is pretreated in an oxygen 20 atmosphere of 50% oxygen. The single crystal is cut into slabs and one slab is polished down to a thickness of 100-200 micrometers. A
layer of porous platinum black of between 100 and 200 micrometers thickness is coated on opposite faces of the slab. One electrode is exposed to pure hydrogen and the other electrode Is exposed to room 25 air. Thls platlnum/solid lanthanum fluoride electrolyte/platinum Is expected to exhibit a ùseful open circuit potential ~VOC) of between about 0 . 5 and 1. 0 volts .
75~.
LaF, as a Sensor for Oxygen ~ a) Lanthanium fluoride, as a portion of a single crystal, is machined and polished to the dimensions of ;'. cm in diameter and tO0 5 micrometers in thickness. This disk is placed in an appropriate electrical circuit in an analytical sensing device.
(b) When the sensor is contacted with a mixture of gases containing oxygen, it is expected that it is possible to detect the presence of oxygen between about 0 .1 and 10, 000 ppm .
tc) When the sensor is contacted with aqueous solution contatning oxygen, it is expected that the sensor will detect oxygen between about 0 .1 and l O, 000 ppm .
(d~ The other solid materials of lAAj above (a) through (m) are also expected to be useful sensors for oxygen in the gas phase or 15 the liquid phase.
(e) The composite materials described herein as the single crystal or polycrystal when machined as described in subpart (a~
above, are expected to be able to detect oxygen in a gas phase or in an aqueous solution.
While some embodiments of the invention have been shown and described herein, it will become apparent to those skilled in the art that various modifications and changes can be made in the present invention regarding solid materials for use as electrodes (electrolytes in fuel cell applications, in sensor applications and in catalyst appli-25 cations~ without departing from its spirit and scope. All such modi-fications and changes coming within the scope of the appended claims are intended to be covered thereby.
,
",, .", ~ :., . ~
- ~3~57~
ll. The solid electrolyte fuel celis demand less ~eed gas prepa-ration than the phosphoric aeid cell, which requires a converslon of CQ to H2 via the wa~r-gas shift rear~ion, or the molten carbonate cell, which require~ a carbon dioxide 5 loop due to the use of carbonate ions for ionic transport.
The attraction of developing a ~olid eleetrolyte fuel ceil is its simplicity. However, a high operation ~emperature (ca. tO00C) is by far the most criticat aspec~ of this ~ype of fuel cell. Although high operation temperature produces high-quality exhaust heat that can 10 ~enerate additional electrical power, leading to a hlgh overall system efficiency, maingainlng the integrity of the cell components such as the interconnector is the most difficult challenge.
It is therefore desirable to develop alternative low temperature solid materials and composites for use as solid electrolytes in fuel 15 cells, as solid sensors and as solid catalysts that can be operated in a range of 400~600C or lower (preferably about 200C, especially at ambient temperature]. Some ~f ~he structures described herein have been examined for usefulness as battery electrolytes. However, none of the references cited hereinabove, individually or collectively, 20 disclose or suggest the present invention as deseribed herein. The present invention relates to the design of such low temperature solid electrolyte fuei cells, sensors, or catalysts based on non-oxide solid electroly~es, such as solid solutiorls of lanthanide fluorides (e.g.
LaX~rl-XF2-~XI-. , . . .
,, ~ . . . .
~3iQ)~7~
SUMMARY OF THi INVENTION
The present invention relates to soiid materials which have application as an electrolyte for a fuel ceil, a sensor or a catalyst.
More specifically, the present invention relates to a solid material 5 IAA] for use as an electrolyte for a fuel cell or for a sensor or as a catalyst, each ha~ing a polycrystal or single crystal s~ructure, com-prising:
~a1 a structure of the formula:
10 wherein A is independently selected from lanthanum, cerium, neo-dynium, praseodynium, scandium or mixtures thereof, wherein AF3 is a single crystal or a portion thereof, (b) a structure of the formula:
Pbl _XMX F2_X
15 wnerein M is independently s~lected from potassium, or silver, and x is between about 0 . 0001 and 0 . 25, (c) a structure of the formuia:
Pbl -x B ix F2+x wherein x is defined herein above;
(d) a structure of the formula:
AyBl _yF2+y wherein:
A as defined hereinabove, B is independently selected from strontium, calcium, barium or 25 magnesium, and y is between about 0.0001 and 1 (e) a structure of the formula:
AyBl -y-zLiF2+y+z ~3~5~
wherein A, B and y are as definad hereinabove, ~ is between about 0. 0001 and 0.10 wherein y l ~ is less than or eq~al to 1;
(f) a structure of the formula:
N1 _n_~l~UnCerl~F2~2n+m 5 wherein N is independently selected from calcium, strontium or bar-ium, n is between about 0. 0001 and 0. 05, and m is between about 0 . 0001 and 0 . 35;
tg) a structure of the formula:
PbSn F4 10 with the proviso that PbSnF4 is only useful as a fuel cell electrolyte;
th~ a structure of the formula:
KSn2F5;
(i) a structure of the formula: , ~' Srcl2-K
tj) a structure of the formula:
:
Laol _pF1 +2p wherein p is between about 0.0001 and 0.9999;
~` tk) a structure of the formula:
PbSnFq PhSnOr 20 wherein q and r are each independently from between about 0 . 0001 and 1;
(I) a structure of the formula:
tAOl~5)ytGF2}l_y : wherein A is as defined hereinabove, y is between about 0.0001 and : 25 1, and G is independently selectecl from calcium and magnesium; and (m) a structure of the formula:
~, SmaNdbFcOd ~:' . ... .
~3~;75~
wherein a and b are each independently between about 2.18 and 9.82 and c i5 between about 12 and 29. 45, and d is between about 3 . 25 and 12, with the proviso that a~b is about 12 and c+2d is about 36.
In another aspect, the present invention relates to a process for 5 the preparation of an electrolyte for a fuel cell or for a sensor, which process comprises:
(a) reacting a structure of material [AA] above in an atmosphere comprising a mixture of oxygen and wa~er wherein the water is present in between about 1 and 9996 by weight at between 100 lO and 1000C for between about 10 and 50 hrs.
In another aspect, the present invention relates to a process for the preparation of an electrolyte for a fuei cell or for a sensor, which process comprises: .
(a) subiecting, for instance, about one gram of a structure of lS material [AA] above to a current of about 10 3 amperes per square centimeter at a temperature of between 0 and 400C for a time sufficient to transmit a certain amount of coulombs equivalent to a product of one Faraday (coulombs/mole) times X where X is between about 0 . 001 and 1, depending upon the specific material structure.
In another aspect, the present invention relates to a process ~BB] for preparing a composite consisting essentially o~:
1-y y 3 having a perovskite or a perovskite-type structure as an electrode catalyst in combination with:
2 5 y 1 ~y 2+y s~
- 1 o -as a discontinuous surface coating solid electrolyte wherein A is independently selected from lanthanum, cerium, neodymium, praseo-dymium, or scandium, B is independently selected from strontium, calcium, barium or magnesium, Q is indepenciently selected from 5 nickel, cobalt, iron or manganese, and y is between about 0. 0001 and 1, which process comprises:
~a~ obtaining a particulate of:
l-y y 3 wherein A, B and y are defined hereinabove having an average lO crystal size distribution of between about 50 and 200 Angstroms in dTameter and a surface area of between about 10 and 100 meters 2/grams and formed into a film-like or pellet-like shape having a general thickness of between about 1 ancl 5mm, a pore size of between about 25 and 200 Anstrorns and (b~ reacting the particlulate of step (a) with a vapor comprisi ng:
Ay B 1 -y F2~y wherein A, B and y are defined hereinabove, at about ambient pres-sure at between about 0 and 1000C: for between about 10 and 30 hr.
20 obtain the composite of between about 25 to 1000 microns in ~hickness; and (c) recovering the composite of step (b) having muttiple inter-faces between:
A1_yByQO3 and AyB1 yF2+
25 said composite having a pore size of between about 25 and 200 Angstroms and a surface area of between about 10 and I 00 meters Igram .
.
,, ~5~5~
A preferred embodîment in this process ~BB] is wherein A is lanthanum, B strontium, Q is cobalt, and especially where y is about 0~3. Another preferred embodiment of process ~E3B] is wherein A is selected from cerium or scandium, B is selected from strontium or 5 magnesium, Q is selected from nickel, cobalt or manganese and y is between about 0. 2 and 0. 4.
In another aspect the present invention relates to the use of the composite of Claim 16 selected from electrodelelectrolyte for a fuel cell, a sensor, or a contact catalyst for synthesis or degradation.
The use of the composite material of Claim 28 as an elec-trode/electrolyte for a fuel cell or a sensor.
The use of the composite material of Claim 30 as an oxygen sensor or a fuel cel 1.
In another aspect the present invention relates to the process lS for the generation of electricity, which process comprises:
~ a) contacting a solid electrolyte of EAA] above or :prepared by process [BB] above with a fuel at between about 0 and 1000C.
In another aspect the present invention relates to the process described herein wherein the fuel ~or the fuel cell is setected from 20 hydrogen, hydrazine, ammonia, fossil fuels, separate components of fossil fuels, or mixtures thereof, wherein all fuels have a boiling point at ambient temperature of 25~C or less. It is especially useful to obtain a fuel cel I having an operating temperature between about lû and 30C.
In another aspect, the composite material may be prepared by replacin~ the perovskite-type structure of the process [BB] with a ~ .
metal phthalocyanine structure, wherein the metal is selected from iron, cobalt, nickel and the like.
In still another aspect, the perovskite-type electrode (or the metal-phthalocyanine elecl:rode) and the discontinuous fluoride 5 electrolyte of process [BB] are each thin films of between about 1 and 25 microns on a conventional inorganic catalyst support~
BRIEF_DESCRIPTION OF THE DRAWINGS
Figure 1 shows Table 1 as a comparison of varlous types of fuel cel Is .
Figure 2 shows the open clrcuit voltage (VOC) versus time using a slngle crystal of lanthanum fluorlde (LaF3).
Flgure 3 shows a configuration of a fuel cell using, for instance, a single crystal of thinly^machined and poltshed lan~hanium fiuoride.
Figure 4 shows a curve of the open circuit voltage versus time 15 using a single crystal of lanthanum fluoridP (LaF3). Figure 4 is at 0.575 volts using Pd/Pt electrodes.
Figure 5 is a table showing the open circuit voltage tVOc) for alr, nitrogen, oxygen and hydrogen.
Figure 6 is a cross section of a solid material composite for solid 0 electrode/electrolyte having a Pt contact, a sslid coating of an 9 0.7Sr0.3F2.7 with a perovskite-type electrod ( LaO 75rO,3CoO3)~
Figure 6A is an enlarged cross section showing the discontinuous nature of the electrolyte on a pore opening of the porous electrocle.
Figure 7 is a cross section of a solid material composite useful as a solid electrode having a catalyst support, a platinum contact, a solid coating of an electrolyte (e.g., La 75r0 3F2 7) with a solid 7Si~
discontinuous coating of a perovskite-type te.g., LaO 75r0 3CoO3) or a metal phthalocyanine (Co,Ni, or Fe phthalocyanine~ electrode.
Figure 7A is an enlarged cross section showing the discontinuous nature of the electrolyte in contact with the ele~trode on the soiid 5 support.
DETAILED DESCRIPTION OF TIIE
In the present invention, lanthanum fluoride is the solid elec-trolyte of choice for a fuel cell, or a sensor. Its properties are 10 shown below in Table 2, Table 2 PRO PERT I ES OF LaF
Crystal structure: hexagonal space group is P63/mcm -D36h -with twelve formula units per cell, -Melting Point: 1493C, -Density: 5, 936, -Dielectric constant: 14 (at 10MHz), -Thermal conductivity: 0.025 (W cm 1deg 1), -Electrical conductivity ~ 10 7 Q 1cm-1 (at 25C) -Transmits light from the vacuum ultraviolet into the infrared, -The effective Debye temperature is.~360K, -The activation energy for fluorine ion diffusion is ~0 . 45 eV, -Activation energy for the formation of defects: -0 . 07eV, -Birefringence: ~n=0.006, -Thermal expansion coefficient: 11x10 ~ cmicm/C ~c-axis, 25C), a good match is Cu, ' ~3~7~
LaF3 has unique physicochemical properties such as high elec-trical conductivity and high polarizability at room temperature. The Debye temperature of LaF3 is only 360K, while its melting point is as high as 1 766K . The observed phenomena appear to be associated S with the formation of Schottky defects and with the diffusion of defects has the unusual Iy low value of ~0 . 07 eV, and the room tem-perature Schottky defect density is about 101 9/cm3 .
Fluorine in LaF3 usually exists in three magnetically nom-equivalent sites. Covalent bonding predominates in two of the sites.
10 In the third slte, the fluorines make up a layered array with approxi-mately 60% ionic bonding and about 4~ 1r-bonding. The high po-larizability and high conductivity of LaF3 at room temperature is primarily due to the motion of F ions through the latter sites. The relatively small radius of F is almost identical with that of the oxide 15 o2 ion (1.25 A); therefore oxide ions (o2 ions) can substitute for the F ions in LaF3. It has been confirmed the oxycien ion transport through the bulk of a single crystal LaF3 by Auger electron spectroscopy. In other words, the solid electrolyte Lai~3 serves as a supporting eiectrolyte analogous to liquid phase in which oxygen ions 20 can move freely.
Lanthanum Fluoride as a Soiid Electrolyte for F_! Cell :
Traditionaily LaF3 has been extensiv21y used as a F ion selec-tive electrode in electroanalytical chemistry. Recently LaF3 has been applied to a room temperature potentiometric oxygen sensor and to a 25 multifunctional sensor; for humidity, temperature, oxygen gas, and dissolved oxygen. However, no disclosure exists concerning the use of LaF3 material dS a single crystal as a solid electrolyte In a fuel 5~5~
cell. In earlier investigations, it was determined that polycrystalline lanthanum fluoride as a thin film solid electrocle was unreliable and unpredictable. About one of ten electrodes prepared shorted out under laboratory conditions. As is described below, the singie 5 crystal lanthanum fluoricle solid electrolyte was reliable and predictable .
Figure 2 illustrates a result on a LaF3 fuel cell. In this case, a single crystal of between absut 10 and 100 mils is used. As shown in Figure 3, one cm diameter single crystal LaF3 with a thickness of 25 l0 mils was used. A comb-shape noble metal (Pt, Au, or Pd) electrode (21 + 21A) was sputtered on both sides of the LaF3 sample 22. One electrode was exposed to pure hydrogen and the other was exposed to room air. A Pt/Pt system exhibited an open circuTt potential (VOC) of about 0 . 6 volts at room temperature . The result was repeatabla upon 15 on an on/off cycle of hydrogen. When the Pt/oxygen cathode 21 was replaced by a Pd electrode with a different configuratlon, VOC was increased to 0. 88 volts. However, in either case, the observed short circuit currents were in the order of 10 3 Amperes. This small amount of current is due to the fact that, in the electrode 20 configuration used in our experiments, the total area of the triple-interface ~i.e. gas, electrode catalyst, and solid electrolyte) available for electrochemical reactions was extremely small. Current density is greatly increased when a large surface area platinum black is used as an electrode.
The following electrochemical reactions rnay take place at each electrode:
Cathode: 2 + 4e = 20, Anode: 2H2 + 202 - 2H20 + 4e 5 Effect on VOc of Oxygen Partial Pressure Differences Between Working and Counter Electrodes A study was made to determine how a difference in oxygen partial pressures on either side of the solid electrolyte contributed to the measured VOc values. The relation used was 10 VOc = RT/4F In P0 (At electrode #1 ) / P0 tAt electrode #2) where P0 stands for partial pressure of oxygen at the electrode specified, R is the universal gas constant, T Is the temperature in Kelvln, and ; F is Faraday's constant.
However, from the results seen in Fi~ure 4 and in Figure 5 15 tTable 3) the oxygen partial pressure differences do not determine :: .
the measured VOc with air at working electrode and oxygen at the counter electrode. This will confirm the result that the observed VOc - ~ is indeed due to a fuel ce!l function.
Those solid materials containing both lanthanurn and fluorine 20 ~especially structure of formula ta) ), are very attractive as solid electrolytes in low temperatures (10 to 30QC) solid eiectrolyte of fuel cel Is .
In preferred embodlments of material iAA~ above, each of the structures (a) through tm) are each independently preferred as a 25 solid electrolyte for a fuel cell, a solid electrolyte for a sensor or as a catalyst, espeacially as fuel cell or a sensor.
, ~L3~S~
ln a preferred embodiment, the solid material material lAA] of the SUMMARY is selected from structures of formula ~a), (b), (d~, (e) or (j). In another embodiment the solid material of [AA] of the SUMMARY is selected from structures of formula (a), ~b), (f), (h), 5 (j) or (k).
Other preferred embodiments of the solid material include the foi lowing:
[1 l fuel cell of material [AA] above has a useful operational temperature range of between about 0 and 1 000C especially wherein l0 the structure in subpart (a) is AF3 wherein A is lanthanum, and also where the operational temperature Is between about 15 and 30C;
[2] the electrolyte of material [AA] is used in a device as a sensor to detect gases selected from oxygen in the gaseous phase or dissolved in a liquid;
15l3] the electrolyte of material [AA] is used for a sensor wherein the sensor has a useful operating range of between about -40C to + 1000C or [4~ the solid material IAA] above as an electrolyte for a sensor of [AA] above is wherein the oxygen sensor has an operating range 20 of between about 0C and 600C.
In the present invention the solid materials of [AA] are unless otherwise stipulated, individually preferred as a component of a fuel cel I, of a sensor or as a catalyst useful In the interconversion formation and degradation of organlc compounds, nltrogen-containing 25 compouncls and the like.
It is intended that the soli~ materials described herein for use as solld electrolytes for fuel and for sensors optlonally include '~L3Qt3 pretreatment of the surfac& of the solid, preferably structures of formula (a), especially where A is lanthanum as described herein below .
Pretreatment U_~ Oxygen Atmosphere An instrinsic single crystal of LaF3 has a conductivity of 10 7 ohm 1 cm 1 (which is mainly due to F lons) at room temperature. It Is suggested that the oxygen ion conductivity in I aF3 may be in-creased simply by sintering the crystal in an oxygen gas atmosphere because some of F ions may be replaced by o2 ions. Recently, - 10 Yamazoe et al., tsupra) r~ported that the response time of LaF3 oxygen sensor was dramatically improved by the treatment of LaF3 in a stream of air containing 15 torr of water vapor at 1 50C for 12 hr .
This Improvement is presumably due to the formation of a lanthanum oxy fluoride at the surface (the chemical composition may be written - 15 as lanthanum oxyfluoride of the structure [j~ in material lAA] above.
In the present invention, the materials describ~d in the Summary of the Invention (and in S:laim 1 ) are sintered in an oxygen environ-ment at elevated temperature. The material is placed in an oxygen atmosph~re containing from 1 to 99 percent by weight of water.
20 Usually the water present is between about 10 and 30 percent by weight especially about 15 percent by weight. The temperature is usually between about 100 and 1000C, preferably between about 150 and 600C, especially between about 200 and 400C.
It is also possible to pretreat a ~olld material IAA] to enhance its lonic conductivity by contacting the material with a polarizing electrical current. Thus, the electrochemical doping (pumping) of .
;;7~i1 , g oxide ions is achieved by subjecting about 1 gram the material [AA]
to 10 3 amperes per square centimeter for between about 1 to 25 hr at ambient temperature. Stated in another way about 1 gram of the structure of the material [AAl above is subjected to a certain amount 5 of coulombs equivalent to a product of one Faraday (coulombs/mole) times X where X is be~ween about 0. 001 and t a depending on the specific material [AA] structure (a) to (m~. This electrochemical pumping may be performed between about O and 400C.
An E!ectrodelElect o y~te 10 Perovskite-type In general, the electrocatalysts for the above cited low tempera-ture solid electrolyte fuel cell can be noble metals ~e.g. platinum), their alloys or blacks, metal-phthalocyanines, transition metal cata-Iysts (e.g. Ni/NiO), and metallic transition metal oxides (e.g.
15 LaO gSrO lMnO3)0 Particularly, it is of interest to use electronically conductive perovsklte-type oxide: e.g.:
A1 -x Bx Q3 where A, B, Q and x are as defined hereinabove as catalytic 20 electrode materials, especially for the oxygen reaction in conjunction with the tanthanlde fluoride solid electrolyte:
:
- Ax B 1 -x F2+x wherein A is: (La, Ce, Nd, Pr or Sc);
and E3 is: (Sr, Ca, Ba or Mg);
25 and x is between about 0.00l and 1.
An example of such a composite electrode/electrolyte system would be: LaO 75rO 3C03lLao.7sro~3F2~7-- : .
' .
~5~
On this interface the electronically conductive phase (electrode: La~ 75r0 3F~ 7) exist adjaoently to aach other and even may be mixed on an atomic-level by sharing La and Sr atoms.
In designing systems of A1_XBxQ3/AxE~1-xF2~x~
one can choose atoms for A and B in such a way that there is a maximum degree of matching in ~he lattice parame~ers ~nd thermal coefficients of the two phases. Therefore, the composite system A1 _XBx~:)O3lAxBl-xF2~x 10 can be an Ideal site to facilitate the following reaction:
2 + 4e = 2O2, beeause a well defined, stable atomic scale three-phase inter~ace (gas, electrode, electrolyte) can be established in the Al xBxQo3/Axi3~-xF2 tX
The perovskites useful in this invention may be purchased or may fe formed according to the procedures described in the literature e . g ., T . Kudo et ai ., U . S, Patent No. 3, 804, 674 .
A typical perovskite preparation is described below in Example 20 ~-Figure 6 shows the confis3uration of a composite for use in a fuel cell. The perovsklte substrate (porbus oxide) electrode 61 jc treated with a vapor to deposit the fiuoride electrolyte 62 on the surface. As shown in Figure 6A fluoride 62 or 65 will enter the pores of the 25 perovskite and also be on the surface 64 of the perovskite in a discontin(Jous manner. In thi~ way, millions of two material catalytic , ,~
57~.
surfaces sites 66 are created to factlitate the electrochemical reaction at the intersection of the perovskite 61 and fluoride (62 or 65).
Figure 7 shows the configuration of a supported composite for use in a fuel cell. The perovsklte substrate 7t is spray dried onto 5 an inor~anic support 7û such as silica ~horia zirconia magnesia or the like having mechanical stability. The fluoride electralyte 72 is then vapor deposited on the surface of the perovskite 71. As shown in Figure 7A the fluoride electrolyte 72 as a vapor enters the pores of the perovsklte ~1 and the substrate 70 in a discontinuous manner.
lO In this way millions of two-material catalytic surfaces 74 are created to facilltate the eiectrochemical reaction at the intersection of the perovskite 71 and fluoride 72.
~;n~
The present invention also contemplates the use of 15 metal-phthalocyanines in electrode/electrolyte composites. In this embodiment of the invention the metal-phthalocyanine (~-phthalocyanine~ is used to replace the perovskite-type oxide described above on a weight to weight basis and is then combined with the solid electroiyte as is described above. The metal ions (Z-) 20 preferred include iron cobalt nickel and the like.
Typical metal-phthalocyanines in these composites include those described above and for example those and similar ones described by K.V. Kordesch in U~S. Patent No. 3 783 026.
The composites described below in Claims 28 2g~ 30 or 31 arP
preferred .
. , .
. ,~ ; ~.
~3~7S~`
Sensors The use of the structures disclosed herein are described sensors in analiytical devices to determine components in the vapor phase and also in the liquid phase.
These sensors are preferably useful to analyze oxygen, carbon dioxide, methane, ethane, ethylene, ammonia, hydrogen sulfide or the Iike. Lanthanum fluoride is preferred to analyze oxygen in a gaseous phase or in a liquid, preferably an aqueous solution.
The range of the analysis may be from between about a part per 10 billion to lO,000 parts per million in the gas phase tusually performed in the potentiometric mode~. Even high concentratlons of a component, for instance, in the liquid phase determined in the current mode i3ecause the proportionality is linear rather than logrithmic.
For the structures defined above in the summary in a preferred embodiment the solid material for use as an electrolyte in a fuel cell or in a sensor or for use as catalyst is selected from structures of (b), (c), (d), (e), ~f), th), (i), (j), (k), ~I), or (m). A more preferred embodiment of the solid material is selected from the 20 structures of (b~ i (C), (d), or (e) . Another preferred embodiment of the solid material is selected from the structures of (k), (I) or (m).
The following Examples are intended to be illustrative only and ;~ are not to be construed as limiting in any way.
:: :
,:
Formation of Solid Th;n Films and Fuel (:ell Measurements ~aa) As is described in B.C. LaRoy et al., above, lead 75 potassium 25 fluoride 5 . 75 (Pbo 75Ko 25F1 75) is evaporated onto in a thin polycrystalline f71m onto a substrate to a thickness of 25 mils. Pt black Is coated onto the polycrystalline film. One electrode is exposed to pure hydrogen and the other is exposed to room alr. This Ptlsotid etectrode/Pt system is expected to exhibit a useful open circuit, l0 potential (VOc~ of between about 0.5 and 1.0 volts.
(bb) The procedure of subpart laa~ above is repeated, except that the Pbo 75K~ ~5F1 75 is replaced by an equivalent weight of P~.75~3~.25F1 .75~
(cc~ The procedure of subpart (aa) above is repeated, except e Pbo.~5Ko.25Fl,75 is repla ed by an equivalent weight of La,3Sr.7i 2.3~
(dd) The proeedure of subpart (aa) above is repeated, except that the Pbo 75Ko 25F1 75 is replaced by an equivalent weight of LaO 4Sr 5LiF2 5~
~o : (ee) The procedure of subpart (aa) above is: repeated, except e Pboo75Ko,25F1,75 is replaced by an equivalent weight of :
.88U,~2Ce,1F2,~4~ :
(ff) The procedure of subpart (aa) above is repeated, except that the Pbo 75Ko 25F1 75 is replaced by an equivaient weight of 25 PbSnF~
~, ....
' ,~.,~
,~.., ,. ,::, ~3~
(gg) The procedure of subpart (aa) above is repeated, except that the Pbo 7sKo 25F1 75 is replaced by an equivalent weight of KSnF5.
thh) The procedure of subpart taa) above is repeated, except 5 that the Pbo 7sKo 2sF1 75 iS replaced by an equivalent weight of SrC12- KCI.
(ii) The procedure of subpart ~aa) above is repeated, except t e Pbo.75Ko.25Fl.75 is replaced by an equivalent weight of LaO, 7Y Fl, 6 -(jj) The procedure of subpart (aa) above is repeated, except t the Pbo,75Ko.25FI,75 is replaced by an equivalent weight of PbSnF0 3 ~ PbSnOo . 4-~ (kk) The procedure of subpart (aa) above is repeated, except ; the Pbo.75Ko.25Fj.75 is replaced by an equivalent weight of 15 (LaO1 5)0.S~caF2)o-5-(Il) The procedure of subpart (aa) above is repeated, except the Pbo.75Ko.25Fl.75 is replaced by an equivalent weight of Sm6Nd6F1 89 .
In subparts ~bb) to (Il) the fuel cell obtained is expected to 20 generate a useful open circuit potential tVOc) of between about 0.5 and 1 . 0 voits . ~ ~
EXAhiPLE 2 FORI~AATION OF A PEROVSKITE FOR AN ELECTi~ODE
.
A pure lanthanum nickelate crystal Is synthesized by a 25 co-precipitation technique. The starting materials are LatNO3)3-6H2O
and NitNO3~2 6H2O talternatively acetates and chlorides can be used as the starting materials ) . The proper amounts of each nitrate 5~L
required to give ~he desired stoichiome~ry are weighed and dissolved In doubly disttiled water to remove Na+ and separated quickly by a centrlfuge teGhnique at 2000 rpm for 'i5 min., since Ni(OH)2 tends to dlssolve at pH-7. Thls procPss is repe,ateci several times. The 5 obtained precipitates are dried in an oven at 1 00C overnight. The dried powder is ~hen put in the furnace at 800C for 16 hours in an 2 atmosphere. The electrode is made by pressing the powders into 13mm diameter pellet (Beckman model K-13 die) at a pressure of 300kg cm 2, The pellet is sintered a~ 750C in an 2 atmosphere for 48 q hours and the perovskite pellet is recovered.
A thin film tabout 100 mlcrometers) of LaO 5SrO 5F2 5 iS
prepared on the perovskite layer by conventional vacuum evaporation (LeRoy et al. ) using pure materia~s of lanthanum fluoride and strontium fluoride in a tungsten boat applying a current of about 40 15 amperes in a high vacuum of abous 10 torr. The composite obtained is expected to have a useful open ircuit potential of between about 0. 5 and 1 . 0 volts .
A Porous Substrate-LaO 5SrO.5coo3 ~film) LaO,5S o,5 2.5 20 bv S~raY Pvrolvsis/Vacuum Evaporation or Reactive S~utterina , _~
taa) A thin layer of a perovskite oxide is prepared on a porous substrate 5e.g. alumina, zirronia oxide with pore size of abut 100 A
with a ~hickness 1-2 mm) by a spray pyrolysis. As an exampie, the 50~ Sr doped LaCoO3 is prepared as follows: 8.5g Sr(NO3)2, 23.39 25 Co(NO3)2-~H2O and 17.81g La(iNO3~3~6H2O (alternatively acetates and chiorldes can be used as the starting materials) ara dissolved in dlsltllled wat~r and sprayed onto the hot porous substrate ~about 10 * l~rade-mark , I ", !
cm by 10 cm) at a flow rate of about 10 mL/min. The homogeneous constituent is then decomposed at 250C, followed by quenching oxygen and heating 500C, in air for 3hr. The perovskite catalyst loadin~ should be about 10mg/cm2. Then, a thin film ~about 100~1m) 5 of LaO 5SrO 5F2 5 is prepared on the perovskite layer by a vacuum evaporatlon using pure materials of LaF3 and SrF2 in a tungsten boat and applying a current of about 40 Amperes in high vacuum of about t0 7 torr. Alternatively pure metal targets can be used in a sputtering process in a low pressure fluorine atmosphere (e.g. 10 m l0 torr). The obtained fuel cell is expected to generate an open circuit potential (VOC) of between about 0 . 5 and 1 . 0 volts . tSee Figure 6, 6A, 7, 7A ) .
In the above (aa) subpart the reaction i5 repeated using an equivalent weight of nickel phthalocyanine for the perovskite. The 15 composite formed is expected to have a useful open circult potential of between about 0. 5 and 1 . 0 volts .
:
: FORMATION OF A SINGLE CRYSTAL BASED FUEL CELL
A single crystal of lanthanum fluorlde is pretreated in an oxygen 20 atmosphere of 50% oxygen. The single crystal is cut into slabs and one slab is polished down to a thickness of 100-200 micrometers. A
layer of porous platinum black of between 100 and 200 micrometers thickness is coated on opposite faces of the slab. One electrode is exposed to pure hydrogen and the other electrode Is exposed to room 25 air. Thls platlnum/solid lanthanum fluoride electrolyte/platinum Is expected to exhibit a ùseful open circuit potential ~VOC) of between about 0 . 5 and 1. 0 volts .
75~.
LaF, as a Sensor for Oxygen ~ a) Lanthanium fluoride, as a portion of a single crystal, is machined and polished to the dimensions of ;'. cm in diameter and tO0 5 micrometers in thickness. This disk is placed in an appropriate electrical circuit in an analytical sensing device.
(b) When the sensor is contacted with a mixture of gases containing oxygen, it is expected that it is possible to detect the presence of oxygen between about 0 .1 and 10, 000 ppm .
tc) When the sensor is contacted with aqueous solution contatning oxygen, it is expected that the sensor will detect oxygen between about 0 .1 and l O, 000 ppm .
(d~ The other solid materials of lAAj above (a) through (m) are also expected to be useful sensors for oxygen in the gas phase or 15 the liquid phase.
(e) The composite materials described herein as the single crystal or polycrystal when machined as described in subpart (a~
above, are expected to be able to detect oxygen in a gas phase or in an aqueous solution.
While some embodiments of the invention have been shown and described herein, it will become apparent to those skilled in the art that various modifications and changes can be made in the present invention regarding solid materials for use as electrodes (electrolytes in fuel cell applications, in sensor applications and in catalyst appli-25 cations~ without departing from its spirit and scope. All such modi-fications and changes coming within the scope of the appended claims are intended to be covered thereby.
,
Claims (25)
PROPERTY OF PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A use of a solid material as an electrolyte for a fuel cell each solid material having a polycrystal or single crystal structure, comprising:
(a) a structure of the formula:
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; wherein AF3 is a single crystal or a portion thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein.
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1;
wherein the solid material as an electrolyte is a thin layer having one side coated with a noble metal which is in contact with a gaseous fuel for a fuel cell and the other side of the thin solid material for the electrolyte is also coated with a noble metal which is in contact with gaseous oxygen, or air or mixtures thereof.
(a) a structure of the formula:
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; wherein AF3 is a single crystal or a portion thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein.
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1;
wherein the solid material as an electrolyte is a thin layer having one side coated with a noble metal which is in contact with a gaseous fuel for a fuel cell and the other side of the thin solid material for the electrolyte is also coated with a noble metal which is in contact with gaseous oxygen, or air or mixtures thereof.
2. A use of a solid material as an electrolyte for a fuel cell having a single crystal structure, comprising (a) a structure of the formula:
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein:
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1.
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein:
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1.
3. The use of a solid material as an electrolyte for a fuel cell of Claim 2 wherein the single crystal has a thickness of between about 100 micrometers and 2.5 millimeters.
4. The use of a solid material as an electrolyte for a fuel cell of Claim 1 wherein the fuel cell has a useful operational temperature range of between about 0 and 1000°C.
5. The use of a solid material of Claim 4 is useful as an electrolyte wherein the structure in subpart (a) is AF3 wherein A is lanthanum as a single crystal.
6. The use of a solid material as an electrolyte of Claim 5 wherein the operational temperature is between about 15 and 30°C.
7. The use of a solid material of Claim 1 wherein the solid material as a single crystal has a thickness of between about 100 to 200 micrometers.
8. The use of a solid material wherein the solid material has a thickness of between about 10 to 100 mils.
9. The use of a composite in a fuel cell said solid composite consisting essentially of:
A1-yByQO3 having a perovskite or a perovskite-type structure as a solid electrode catalyst in combination with:
AyB1-yF2+y as a discontinuous surface coating solid electrolyte on the perovskite wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, or scandium, B is independently selected from strontium, calcium, barium or magnesium, Q is independently selected from nickel, cobalt, iron or manganese, and y is between about 0.0001 and 1 wherein the perovskite has an average size distribution of between about 50 and 200 Angstroms in diameter and the composite layer of between about 25 to 1000 microns in thickness;
said composite having multiple interfaces between:
A1-yByQO3 and AyB1-yF2+y and a pore size of between about 25 and 200 Angstroms and a surface area of between about 10 and 100 meters 2/gram.
A1-yByQO3 having a perovskite or a perovskite-type structure as a solid electrode catalyst in combination with:
AyB1-yF2+y as a discontinuous surface coating solid electrolyte on the perovskite wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, or scandium, B is independently selected from strontium, calcium, barium or magnesium, Q is independently selected from nickel, cobalt, iron or manganese, and y is between about 0.0001 and 1 wherein the perovskite has an average size distribution of between about 50 and 200 Angstroms in diameter and the composite layer of between about 25 to 1000 microns in thickness;
said composite having multiple interfaces between:
A1-yByQO3 and AyB1-yF2+y and a pore size of between about 25 and 200 Angstroms and a surface area of between about 10 and 100 meters 2/gram.
10. The use of a composite of Claim 9 which further includes a suitable inorganic support.
11. A process for the generation of electricity, which process comprises:
contacting a solid material having a polycrystal or single crystal structure, comprising (a) a structure of the formula:
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein:
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1 with a suitable fuel at between 0 and 1000°C.
contacting a solid material having a polycrystal or single crystal structure, comprising (a) a structure of the formula:
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein:
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1 with a suitable fuel at between 0 and 1000°C.
12. The process of Claim 11 wherein the fuel for the fuel cell is selected from hydrogen, hydrazine, ammonia, fossil fuels, separate components of fossil fuels, or mixtures thereof, wherein all fuels have a boiling point at ambient temperature of 250°C or less.
1.3. The process of Claim 12 wherein in step (a) the operating temperature is between about 10 and 30°C.
14. The use of a solid material of Claim 1 wherein a single crystal has a thickness of between about 10 and 100 mils.
15. The use of a solid material of Claim 14 wherein a single crystal is LaF3.
16. The use of a solid material of Claim 15 wherein the LaF3 has a thickness of about 100 micrometers.
17. The use of a solid material of Claim l wherein the solid material used as an electrolyte in a fuel cell has a useful operational temperature of between 0 and 1000°C.
18. The use of a solid material of Claim 17 wherein the solid material is LaF3.
19. The use of a solid material of Claim 17 wherein the useful operational temperature is between about 15 and 30°C.
20. A process for improving the ionic conductivity for a solid material having a polycrystal or monocrystal structure, which process comprises:
(a) pretreating a solid material having a structure of the formula:
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; wherein AF3 is a single crystal or portion thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein:
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1, by contacting the solid material with a polarizing electrical current wherein about 1 gram of solid material is subjected to about 10-3 amperes per square centimeter for between about 1 to 15 hr.
at between about 0 and 400°C.
(a) pretreating a solid material having a structure of the formula:
wherein A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; wherein AF3 is a single crystal or portion thereof; or (b) a structure of the formula:
AyB1-yF2+y wherein:
A is as defined hereinabove, B is independently selected from strontium, calcium, barium or magnesium, and y is between about 0.0001 and 1, by contacting the solid material with a polarizing electrical current wherein about 1 gram of solid material is subjected to about 10-3 amperes per square centimeter for between about 1 to 15 hr.
at between about 0 and 400°C.
21. The process of Claim 20 wherein the solid material is lanthanum fluoride.
22. The use of a solid material of Claim 1 wherein in (b) A is lanthanum and B is strontium.
23. The use of a solid material of Claim 22 wherein y is 0.5.
24. The use of a solid material of Claim 22 wherein y is 0.7.
25. The use of a solid material of Claim 22 wherein y is 0.9.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000553723A CA1305751C (en) | 1987-12-08 | 1987-12-08 | Solid compositions for fuel cells, sensors and catalysts |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000553723A CA1305751C (en) | 1987-12-08 | 1987-12-08 | Solid compositions for fuel cells, sensors and catalysts |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1305751C true CA1305751C (en) | 1992-07-28 |
Family
ID=32996909
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000553723A Expired - Fee Related CA1305751C (en) | 1987-12-08 | 1987-12-08 | Solid compositions for fuel cells, sensors and catalysts |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1305751C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019245929A1 (en) * | 2018-06-15 | 2019-12-26 | Massachusetts Institute Of Technology | Perovskites for catalyzing oxygen evolution |
-
1987
- 1987-12-08 CA CA000553723A patent/CA1305751C/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019245929A1 (en) * | 2018-06-15 | 2019-12-26 | Massachusetts Institute Of Technology | Perovskites for catalyzing oxygen evolution |
| US11220753B2 (en) | 2018-06-15 | 2022-01-11 | Massachusetts Institute Of Technology | Perovskites for catalyzing oxygen |
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