WO2014012673A1 - Solid oxide cell oxygen electrode with enhanced durability - Google Patents
Solid oxide cell oxygen electrode with enhanced durability Download PDFInfo
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- WO2014012673A1 WO2014012673A1 PCT/EP2013/002150 EP2013002150W WO2014012673A1 WO 2014012673 A1 WO2014012673 A1 WO 2014012673A1 EP 2013002150 W EP2013002150 W EP 2013002150W WO 2014012673 A1 WO2014012673 A1 WO 2014012673A1
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- Prior art keywords
- layer
- electrode layer
- forming
- electrolyte layer
- electrolyte
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- 239000007787 solid Substances 0.000 title claims abstract description 63
- 239000001301 oxygen Substances 0.000 title description 63
- 229910052760 oxygen Inorganic materials 0.000 title description 63
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title description 60
- 239000003792 electrolyte Substances 0.000 claims abstract description 280
- 239000002019 doping agent Substances 0.000 claims abstract description 121
- 238000000034 method Methods 0.000 claims abstract description 50
- 238000005245 sintering Methods 0.000 claims description 109
- 229910001233 yttria-stabilized zirconia Inorganic materials 0.000 claims description 104
- 229910002075 lanthanum strontium manganite Inorganic materials 0.000 claims description 66
- 229910052684 Cerium Inorganic materials 0.000 claims description 58
- FVROQKXVYSIMQV-UHFFFAOYSA-N [Sr+2].[La+3].[O-][Mn]([O-])=O Chemical compound [Sr+2].[La+3].[O-][Mn]([O-])=O FVROQKXVYSIMQV-UHFFFAOYSA-N 0.000 claims description 55
- 229910052791 calcium Inorganic materials 0.000 claims description 49
- 239000000446 fuel Substances 0.000 claims description 45
- 229910052727 yttrium Inorganic materials 0.000 claims description 33
- 229910052749 magnesium Inorganic materials 0.000 claims description 26
- 229910052772 Samarium Inorganic materials 0.000 claims description 16
- 229910002651 NO3 Inorganic materials 0.000 claims description 12
- 238000007650 screen-printing Methods 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical class [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 5
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical class [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 5
- 150000002823 nitrates Chemical class 0.000 claims description 5
- 229910021653 sulphate ion Inorganic materials 0.000 claims description 5
- 238000005868 electrolysis reaction Methods 0.000 claims description 4
- 238000004528 spin coating Methods 0.000 claims description 4
- 238000005507 spraying Methods 0.000 claims description 4
- 230000002730 additional effect Effects 0.000 claims 2
- 230000015572 biosynthetic process Effects 0.000 abstract description 12
- 238000009792 diffusion process Methods 0.000 abstract description 8
- 239000007857 degradation product Substances 0.000 abstract description 3
- 230000000087 stabilizing effect Effects 0.000 abstract description 2
- 210000004027 cell Anatomy 0.000 description 118
- 238000010345 tape casting Methods 0.000 description 22
- MCMNRKCIXSYSNV-UHFFFAOYSA-N ZrO2 Inorganic materials O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 21
- 229910052742 iron Inorganic materials 0.000 description 18
- 238000002360 preparation method Methods 0.000 description 12
- 239000000843 powder Substances 0.000 description 11
- 239000000463 material Substances 0.000 description 10
- 239000002002 slurry Substances 0.000 description 10
- 239000011572 manganese Substances 0.000 description 9
- 230000015556 catabolic process Effects 0.000 description 8
- 238000006731 degradation reaction Methods 0.000 description 8
- 238000005470 impregnation Methods 0.000 description 8
- 230000004888 barrier function Effects 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 229910002076 stabilized zirconia Inorganic materials 0.000 description 7
- FFQALBCXGPYQGT-UHFFFAOYSA-N 2,4-difluoro-5-(trifluoromethyl)aniline Chemical compound NC1=CC(C(F)(F)F)=C(F)C=C1F FFQALBCXGPYQGT-UHFFFAOYSA-N 0.000 description 6
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 6
- 239000000725 suspension Substances 0.000 description 6
- 239000001257 hydrogen Substances 0.000 description 5
- 229910052739 hydrogen Inorganic materials 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 230000010287 polarization Effects 0.000 description 5
- RUDFQVOCFDJEEF-UHFFFAOYSA-N yttrium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Y+3].[Y+3] RUDFQVOCFDJEEF-UHFFFAOYSA-N 0.000 description 5
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 4
- 229910007735 Zr—Si Inorganic materials 0.000 description 4
- 239000007795 chemical reaction product Substances 0.000 description 4
- 239000002131 composite material Substances 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 230000005611 electricity Effects 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
- 239000008188 pellet Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 238000000151 deposition Methods 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- 239000002001 electrolyte material Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 229910052746 lanthanum Inorganic materials 0.000 description 3
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 3
- 239000012528 membrane Substances 0.000 description 3
- -1 oxygen ions Chemical class 0.000 description 3
- 230000002441 reversible effect Effects 0.000 description 3
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 2
- 150000001768 cations Chemical class 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 239000012153 distilled water Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000002737 fuel gas Substances 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 229920002037 poly(vinyl butyral) polymer Polymers 0.000 description 2
- 229920000036 polyvinylpyrrolidone Polymers 0.000 description 2
- 239000001267 polyvinylpyrrolidone Substances 0.000 description 2
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 description 2
- 239000013074 reference sample Substances 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 239000007784 solid electrolyte Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910017060 Fe Cr Inorganic materials 0.000 description 1
- 229910002544 Fe-Cr Inorganic materials 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000000498 ball milling Methods 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 210000005056 cell body Anatomy 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- UPHIPHFJVNKLMR-UHFFFAOYSA-N chromium iron Chemical compound [Cr].[Fe] UPHIPHFJVNKLMR-UHFFFAOYSA-N 0.000 description 1
- 230000007850 degeneration Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000002847 impedance measurement Methods 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 229910001092 metal group alloy Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 1
- 229910001928 zirconium oxide Inorganic materials 0.000 description 1
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
- H01M8/1253—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 the electrolyte containing zirconium oxide
-
- 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
- H01M4/8605—Porous electrodes
- H01M4/8621—Porous electrodes containing only metallic or ceramic material, e.g. made by sintering or sputtering
-
- 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
- H01M4/88—Processes of manufacture
- H01M4/8825—Methods for deposition of the catalytic active composition
- H01M4/8828—Coating with slurry or ink
- H01M4/8835—Screen printing
-
- 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
- H01M4/88—Processes of manufacture
- H01M4/8825—Methods for deposition of the catalytic active composition
- H01M4/886—Powder spraying, e.g. wet or dry powder spraying, plasma spraying
-
- 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
- H01M4/88—Processes of manufacture
- H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
- H01M4/8882—Heat treatment, e.g. drying, baking
- H01M4/8885—Sintering or firing
- H01M4/8889—Cosintering or cofiring of a catalytic active layer with another type of layer
-
- 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
- H01M4/88—Processes of manufacture
- H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
- H01M4/8892—Impregnation or coating of the catalyst layer, e.g. by an ionomer
-
- 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
- H01M2300/0077—Ion conductive at high temperature based on zirconium oxide
-
- 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
- H01M2300/0088—Composites
-
- 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
Definitions
- the present invention relates to a solid oxide cell with an enhanced durability, and to methods for preparing same.
- Solid oxide cells are well known in the art and come in various designs. Typical configurations include a flat plate design and a tubular design, wherein an electrolyte layer is sandwiched between two electrode layers. During operation, usually in a temperature range of from 500°C to 1100°C, one electrode is in contact with oxygen or air and the other electrode is in contact with a fuel gas.
- Solid oxide cells include solid oxide fuel cells (SOFC's) and solid oxide electrolysis cells (SOEC's).
- a 'reversible' solid oxide cell is a cell that can usually consume a fuel gas, such as hydrogen, to produce electricity, and can be reversed so as to consume electricity to produce a gas.
- a fuel gas such as hydrogen
- a hydrogen fuel cell for example, uses hydrogen (H 2 ) and oxygen (0 2 ) to produce electricity and water (H 2 0); a reversible hydrogen fuel cell could also use electricity and water to produce hydrogen and oxygen gas. Due to the identical layer design of the cell, the same cell may therefore be in principle used for both applications, and is conseguently referred to as a 'reversible' cell.
- the oxygen electrode is the cathode where a reduction of oxygen to oxygen ions takes place.
- this electrode is referred to as the anode as here the process is now an oxidation process.
- a wide range of material properties for SOFC cathodes and SOEC anodes, i.e. the oxygen electrodes of the respective cell, is required in order to operate the cell with a sufficient life time as demanded by the industry today.
- the oxygen electrodes require high ionic conductivity, high electronic conductivity, good catalytic activity towards oxygen reduction, a thermal expansion coefficient (TEC) that matches the TEC of the other materials of the cell, thermal stability, and chemical stability.
- TEC thermal expansion coefficient
- LSM lanthanum-strontium-manganite
- YSZ oxygen ion conductive material
- electrolyte layer made of an oxygen ion conductive solid oxide, such as YSZ or doped ceria.
- the reaction takes place at the so-called triple phase boundaries where electrode material, electrolyte material and the reactive gas are in contact with each other. Efficient gas diffusion and increased contact areas between the electrolyte and the electrodes are therefore important.
- the performance of the oxygen electrode is mainly determined by the resistance present at the oxygen electrode-electrolyte interface. It is desirable to reduce the interfacial resistance and to increase the number of triple phase boundaries.
- the interfacial resistance is for example increased due to degradation products which are formed by a reaction between electrolyte material and electrode material.
- degeneration products include, for example, lanthanum zirconate La 2 Zr 2 0 7 (LZO), strontium zirconate (SZO), monoclinic Zr0 2 , or oxides of La-Zr-Si and Sr-Zr-Si.
- LZO or SZO lanthanum zirconate La 2 Zr 2 0 7
- SZO strontium zirconate
- monoclinic Zr0 2 oxides of La-Zr-Si and Sr-Zr-Si.
- the formation of zirconates (LZO or SZO) or monoclinic zirconia is increased at high temperatures which may occur during the manufacture of the cell when sintering the cell body after formation in its green, i.e. pre-sintered state.
- the formation of LZO or SZO is also increased during cell testing
- barrier layers at the interface in between the electrolyte layer and the electrode layer to prevent unwanted side reactions.
- the application of a barrier layer requires one additional step during the manufacture of the cell and increases the resistance of the cell due to the additional layer itself and due to the additional interface between the barrier layer and the electrolyte layer (which introduces additional interface resistance).
- diffusion takes place between the barrier layer and the electrolyte layer, and said diffu- sion layer reduces the conductivity of the cell.
- EP 2194597 art relates to a solid oxide cell obtainable by a process which comprises the steps of:
- the one or more oxygen electrode layers comprising a composite of lanthanum strontium manganite and stabilized zirconia to provide a complete solid oxide cell
- JP 2002/015754 relates to a solid electrolyte fuel cell comprising an air electrode made of a perovskite complex oxide containing at least lanthanum and manganese, a solid electrolyte primarily formed of zirconium oxide, and further a fuel electrode.
- US 2006/199057 A1 discloses a solid oxide fuel cell comprising a single cell having an air electrode disposed on a surface of an electrolyte membrane and a fuel electrode disposed on the other surface of the electrolyte membrane, and an interconnector having a role of electrical connection;
- the electrolyte membrane is provided with a first layer composed of a material having an oxygen-ionic conductivity of S1 on the air-electrode side, and a second layer composed of a material containing at least zirconia and having an oxygen-ionic conductivity of S2 on the fuel-electrode side; and wherein the oxygen-ionic conductivity of S1 on the air-electrode side and the oxygen- ionic conductivity of S2 on the fuel-electrode side have a relationship of S1>S2.
- the present invention provides in embodiments a method of producing a solid oxide cell, comprising the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; or a. l.2)
- electrolyte layer comprises yttria stabilized zirconia
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- said electrode layer comprises lanthanum strontium manganite
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- electrolyte layer comprises yttria stabilized zirconia
- the present invention further provides a method of producing a solid oxide cell, compris- ing the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- electrolyte layer comprises yttria stabilized zirconia
- the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- the present invention also provides a method of producing a solid oxide cell, comprising the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- electrolyte layer comprises yttria stabilized zirconia
- said electrode layer comprises lanthanum strontium manganite
- said electrode layer comprises lanthanum strontium manganite
- electrolyte layer on top of said electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- the electrode layer which comprises lanthanum strontium manganite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- the present invention moreover provides a method of producing a solid oxide cell, com ⁇ prising the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
- electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
- said electrode layer comprises lanthanum strontium manganite
- said electrode layer comprises lanthanum strontium manganite
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
- electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
- the present invention also provides a solid oxide cell, being obtainable by any of the above methods.
- Preferred embodiments are set forth in the subclaims and the following detailed description.
- Figure 1 relates to a solid oxide cell in accordance with the present invention, where the dopant/dopants are enriched in the region close to the oxygen electrode - electrolyte interface.
- Figure 2 illustrates a solid oxide cell in accordance with the present invention, where the yttria stabilized zirconia electrolyte layer is replaced with doped YSZ.
- Figure 3 illustrates the serial resistance of the symmetrical cells tested at 750°C in air for periods up to 200 hours.
- Figure 4 illustrates the polarization resistance of the symmetrical cells tested at 750°C in air for periods up to 200 hours.
- the present invention provides a method of producing a solid oxide cell, wherein an additional layer is formed in between the electrolyte layer and the electrode layer which comprises lanthanum strontium manganite. More specifically, the present invention provides a method of producing a solid oxide cell, comprising the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; or a.l.2)
- electrolyte layer comprises yttria stabilized zirconia
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- said electrode layer comprises lanthanum strontium manganite
- said electrode layer comprises lanthanum strontium manganite
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- electrolyte layer comprises yttria stabilized zirconia
- an additional layer is formed on the electrolyte layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant.
- Said dopants are present at the interface of the electrolyte and electrode and prevent especially the diffusion of Mn from the second electrode layer into the electrolyte, stabilizing the LSM and thereby preventing the formation of unwanted degradation products such as LZO or SZO.
- the additional layer and the electrolyte layer form one layer which from a macroscopic point of view appears to be an electrolyte layer with the dopant enriched on one surface thereof rather than a separate barrier layer on top of the electrolyte layer.
- the present invention therefore provides an improved structure which prevents diffusion especially of Mn from the electrode layer into the electrolyte layer at the interface where the dopant is enriched.
- the so obtained improved structure reduces or avoids the increased internal resistance and conductivity losses which occurs in case of a separate barrier layer as proposed in the prior art.
- the dopant provided with the additional layer is capable to stabilize the LSM- YSZ interface and prevents unwanted reactions between the electrode material and electrolyte material without the disadvantages of diffusion and without the additional increased internal resistance and conductivity losses.
- the cell may be produced by using the first formed layer as a support layer. Usually, this layer is relatively thick, as compared to the other layers, to provide additional mechanical support. Alternatively, if desired, an additional support may be used if desired, on which the first layer is applied.
- the first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layers.
- the first electrode layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- said electrode layer comprises lanthanum strontium manganite
- the additional layer and the electrolyte layer form the specific structure as outlined above, i.e. in the electrolyte structure, the dopant is enriched on the surface opposite the electrolyte layer surface in contact with the first electrode layer.
- the second electrode layer which comprises lanthanum strontium manganite, is applied.
- the dopant effectively reduces or suppresses the Mn diffusion from the electrode layer which comprises lanthanum strontium manganite into the electrolyte layer.
- the electrolyte layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of:
- electrolyte layer comprises yttria stabilized zirconia
- first electrode layer on top of said electrolyte layer
- additional layer on said electrolyte layer on the side opposite of the first electrode layer, wherein the additional layer comprises yttria stabilized zirco- nia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- said electrode layer comprises lanthanum strontium manganite
- the electrode layer which comprises lanthanum strontium manganite is the first formed layer which preferably functions as the support layer for all other layers if no additional support is used.
- the additional layer has to be applied on said layer first, followed by the formation of the electrolyte layer, so as to provide a dopant enriched surface of the electrolyte at the interface to the electrode comprising lanthanum strontium manganite.
- the method comprises the steps of:
- said electrode layer comprises lanthanum strontium manganite
- the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- electrolyte layer comprises yttria stabilized zirconia
- the dopants are generally selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y.
- Preferred dopants are oxides of Fe, Mg or Ce, more preferably Fe or Mg.
- the most preferred dopant is Fe.
- the amount of dopants being in the range of 0.1 - 10 cat.% (cation percentage), preferably in the range of 0.3 - 5 cat.% and more preferably in the range of 0.5 - 2 cat.%.
- the cation percentage is based on all metal elements but excludes oxygen.
- the additional layer on the electrolyte layer is as thin as possible.
- the additional layer has preferably a thickness of 5 pm or less, and more preferably a thickness of 2 pm or less.
- the electrode which comprises lanthanum strontium manganite further preferably comprises yttria stabilized zirconia, and even more preferably comprises yttria stabilized zir- conia and a dopant.
- Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y.
- the dopant is directly applied on top of the electrolyte layer instead of being part of an additional layer.
- the formation of the additional layer prior to sintering can be omitted, thereby being more cost effective due to less material being used.
- the present invention provides a method of producing a solid oxide cell, comprising the steps of: a.1.1)
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- electrolyte layer comprises yttria stabilized zirconia
- the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- the cell may be produced by using the first layer as a support layer.
- this layer is relatively thick, as compared to the other layers, to provide mechanical support.
- an additional support may be used if desired, on which the first layer is applied.
- the first electrode layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- the electrolyte layer is the first formed layer which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of
- electrolyte layer comprises yttria stabilized zirconia
- the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- the dopant is directly applied on top of the electrolyte layer instead of being part of an additional layer.
- the formation of the additional layer can be omitted, thereby being more cost effective due to less material and one production step less.
- the dopant is applied by a method such as screen printing, spraying or spin coating.
- the dopant is selected form the group consist- ing of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y.
- Preferred dopants are oxides of Ce, Mg or Fe, more preferably Fe or Mg. The most preferred dopant is Fe.
- the heat treatment step is preferably carried out at a temperature of from 600 to 1250°C, more preferably at a temperature of from 600 to 1000°C, more preferably of from 650 to 900°C, and even more preferably at a temperature of from 700 to 850°C.
- the electrode which comprises lanthanum strontium manganite preferably comprises yttria stabilized zirconia, and even more preferably comprises yttria stabilized zirconia and a dopant.
- Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y.
- the second electrode layer which comprises lanthanum strontium manganite is impregnated with at least one dopant after the sintering step. More specifically, the present invention provides a method of producing a solid oxide cell, comprising the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- electrolyte layer comprises yttria stabilized zirconia
- said electrode layer comprises lanthanum strontium manganite
- said electrode layer comprises lanthanum strontium manganite
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- the electrode layer which comprises lanthanum strontium man- ganite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- the cell may be produced by using the first layer as a support layer.
- an additional support may be used if desired, on which the first layer is applied.
- the first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layers.
- the first electrode layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- said electrode layer comprises lanthanum strontium manganite
- the electrode layer which comprises lanthanum strontium manganite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- the electrolyte layer is the first formed layer which preferably functions as the support layer for all other layers if no additional support is used, independent of the use of an additional support, the method comprises the steps of:
- electrolyte layer comprises yttria stabilized zirconia
- said electrode layer comprises lanthanum strontium manganite
- the electrode layer which comprises lanthanum strontium mangan- ite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- the second electrode layer comprises lanthanum strontium manganite forms the first layer which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of:
- said electrode layer comprises lantha- num strontium manganite
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- the electrode layer which comprises lanthanum strontium mangan- ite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- the second electrode layer is impregnated with at least one dopant after the sintering step.
- the dopant can advantageously be employed in form of a solution suitable for impregnation of the electrode.
- the dopant impregnated into the second electrode layer is in form of a nitrate, sulphate or chloride of Ca, Ce, Fe, Gd, Mg, Sm and Y. More preferred are dopants of Fe, Mg or Ce in form of a nitrate, sulphate or chloride, even more preferably dopants of Fe or Mg in form of a nitrate, sulphate or chloride.
- the most preferred dopant is Fe in form of a nitrate, sulphate, or chloride.
- the impregnation of the electrode can be carried out in one step. Alternatively, the impregnation can be repeatedly carried out until a predetermined amount of dopant is achieved.
- the electrode which comprises lanthanum strontium manganite further comprises yttria stabilized zirconia and even more preferably comprises yttria stabilized zirconia and a dopant.
- Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y.
- the present invention provides a method of producing a solid oxide cell, wherein the dopant is already comprised in the electrolyte layer. Thus, additional steps such as the application of an additional layer or the impregnation of the second electrode layer are not necessary. More specifically, the present invention provides a method of producing a solid oxide cell, comprising the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
- electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
- said electrode layer comprises lanthanum strontium manganite
- said electrode layer comprises lanthanum strontium manganite
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
- electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
- the first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layer.
- the cell may be produced by using the first layer as a support layer. Usually, this layer is relatively thick, as compared to the other layers, to provide mechanical support. Alternatively, if desired, an additional support may be used if desired, on which the first layer is applied.
- the first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layers.
- the first electrode layer is the first layer being formed, which preferably functions as the support layer for all other layers if no additional support is used. Independent of the use of an additional support, the method comprises the steps of:
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of
- said electrode layer comprises lanthanum strontium manganite
- the electrolyte layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of: a.1.2)
- electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
- said electrode layer comprises lanthanum strontium manganite
- the electrode layer which comprises lanthanum stron- tium manganite forms the first layer which preferably functions as the support layer for all other layers if no additional support is used.
- the method comprises the steps of:
- said electrode layer comprises lantha- num strontium manganite
- electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
- electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
- said elec- trode layer comprises lanthanum strontium manganite
- the dopant is already comprised in the electrolyte layer. Thus, additional steps such as the application of an additional layer or the impregnation of the second electrode layer are not necessary. However, the amount of dopant has to be increased so as to ensure that in the composition, the amount of dopant present on the interface is still sufficient to suppress any unwanted reactions.
- Preferred dopants are oxides of Fe, Mg or Ce, more preferably Fe or Mg. The most preferred dopant is Fe.
- the electrode which comprises lanthanum strontium manganite further preferably comprises yttria stabilized zirconia, and even more preferably comprises yttria stabilized zir- conia and a dopant.
- Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y.
- the sintering step is preferably carried out at a temperature of from 1000°C and 1500°C, more preferably at a temperature of from 1 100 to 1450°C.
- the composition preferably comprises a composite of LSM and stabilized zirconia. Further preferred is the atomic ratio of manganese to lanthanum and strontium in the LSM being greater than 1 , more preferably being greater than 1 .02. Stabilized zirconia can be yttria, or MgO, or CaO stabilized zirconia or any other material known in the art.
- the thickness of the electrolyte layer in all embodiments is generally in the range of from 1 to 200 ⁇ , preferably from 5 to 150 pm, and more preferably of from 10 to 100 pm. If the electrolyte layer however functions as a support layer, the thickness is preferably in the range of from 30 to 200 pm, preferably from 50 to 150 pm, and more preferably of from 60 to 100 pm.
- each electrode layer in all embodiments is generally in the range of from 5 to 200 pm, preferably from 10 to 150 pm, and more preferably of from 20 to 100 pm. If the respective electrode layer however functions as a support layer, the thickness is preferably in the range of from 30 to 200 pm, preferably from 50 to 150 pm, and more preferably of from 60 to 100 pm.
- the present invention also provides a solid oxide cell, being obtainable by the above methods.
- the solid oxide cell can be used as a solid oxide fuel cell or a solid oxide electrolysis cell.
- the material for the fuel electrode layer can be any material known in the art for a fuel electrode.
- a Ni-stabilized zirconia composite may be used.
- the layer may comprise metal alloy particles, such as Fe-Cr alloy particles.
- the cell may further comprise additional layers, such as a support layer.
- reactions in between LSM of the electrode and YSZ of the electrolyte at the interface can effectively be reduced or prevented, and the formation of especially, zirconates such as LZO, SZO, La-Zr-Si and Sr-Zr-Si is suppressed, due to the presence of a dopant at the interface.
- the dopant ensures that especially the amount of Mn in the electrode is maintained at thus the LSM is stabilized. This results in a reduction of degradation in the SOC (SOFC/SOEC) and an increase in the performance and overall life time of the cell.
- the adhesion between the oxygen electrode and the electrolyte of the solid oxide cell is improved because LSM grains are prevented from detaching themselves from the stabilized zirconia electrolyte surface.
- Table 1 XRD-detected secondary phases formed in the above pellets.
- the numbers in parentheses are the intensity ratios between the secondary phases and the cubic YSZ phase.
- both La 2 Zr 2 0 7 and SrZr0 3 were detected as reaction products for the samples annealed in N 2
- m-Zr0 2 was detected as a reaction product for the samples annealed in air, though the amount of these reaction products vary from sample to sample.
- Both Ce and Fe oxides showed a strong effect in preventing the zirconate formation, as illustrated by the much lower intensity of La 2 Zr 2 0 7 and SrZr0 3 as compared to the reference sample, while Ca, Ce, Mg and Y oxides were effective in preventing the m-Zr0 2 formation.
- Example 1 Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface A solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
- the suspension for tape-casting is manufactured by means of ball milling of powders with polyvinyl pyrrolidone (PVP), polyvinyl butyral (PVB) and ethanol (EtOH) and methyl ethyl ketone (MEK) as additives.
- PVP polyvinyl pyrrolidone
- PVB polyvinyl butyral
- EtOH ethanol
- MEK methyl ethyl ketone
- AS layer The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder.
- the green thickness of the tape-cast layer was in the range of 400 pm.
- the porosity of this layer was in the range of 30% after sintering and reduction.
- a layer The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was approximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
- E1 layer The slurry of E1 layer comprised TZ8Y.
- E2 layer The slurry of E2 layer comprised TZ8Y + 2 cat.% Fe oxide. After tape casting and sintering E1 and E2 layer will become one electrolyte layer (E), with no interface between E1 and E2. The thickness of the E layer was approximately 10 pm.
- the half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100°C/h and left for about 12 hours and to cool to room temperature to form a sintered half cell. After sintering, the electrolyte layer was enriched with Fe close to the surface where the oxygen electrode will be applied.
- An oxygen electrode layer was deposited on the sintered half cell by screen printing an ink comprising a 1 :1 weight ratio mixture of and YSZ on the surface of the electrolyte layer (E). The thickness of the oxygen electrode layer was 20 - 30 ⁇ before sintering.
- Example 2 Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
- a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
- AS layer The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder.
- the green thickness of the tape-cast layer was in the range of 400 pm.
- the porosity of this layer was in the range of 30% after sintering and reduction.
- a layer The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was ap- proximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
- E layer The slurry of E layer comprised TZ8Y. After tape casting and sintering the thickness of the E layer was approximately 10 pm.
- the half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100 °c /h and left for about 12 hours and to cool to room temperature to form a sintered half cell.
- An oxygen electrode layer was deposited on the sintered half cell by screen printing an ink comprising a 1 :1 weight ratio mixture of Lao / sSro ⁇ sMn L osC ⁇ and YSZ on the surface of the electrolyte layer (E).
- the thickness of the oxygen electrode layer was 20 - 30 pm before sintering.
- Example 3 Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
- a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
- AS layer The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder.
- the green thickness of the tape-cast layer was in the range of 400 pm.
- the porosity of this layer was in the range of 30% after sintering and reduction.
- a layer The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was approximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
- E layer The slurry of E layer comprised TZ8Y. After tape casting and sintering the thickness of the E layer was approximately 10 pm.
- the half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100 °c /h and left for about 12 hours and to cool to room temperature to form a sintered half cell.
- An oxygen electrode layer was deposited on the sintered half cell by screen printing an ink comprising a 1 :1 weight ratio mixture of Lao ysSro asMn-i osO ⁇ and YSZ on the surface of the electrolyte layer (E).
- the thickness of the oxygen electrode layer was 20 - 30 pm before sintering.
- Impregnating the oxygen electrode layer with Fe A Fe-Nitrate aqueous solution was made by dissolving 10 g Fe-Nitrate (purity 99.999%) in 100 ml distilled water. The solution was dripped on the surface of the porous oxygen electrode layer by an eye dropper. The impregnation process was repeated at least twice to supply a concentration of 0.5-5 mg Fe/cm 2 on the oxygen electrode surface to obtain a solid oxide cell. 8) Heating the impregnated cell at a temperature of 350°C for 2 hours to decompose the nitrate into oxide.
- Example 4 Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
- a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
- AS layer The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder.
- the green thickness of the tape-cast layer was in the range of 400 pm.
- the porosity of this layer was in the range of 30% after sintering and reduction.
- a layer The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was approximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
- E layer The slurry of E layer comprised TZ8Y + 2 cat.% Fe oxide. After tape casting and sintering the thickness of the E layer was approximately 10 pm.
- the half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100 °c /h and left for about 12 hours and to cool to room temperature to form a sintered half cell.
- An oxygen electrode layer was deposited on the sintered half cell by screen print ⁇ ing an ink comprising a 1 :1 weight ratio mixture of and YSZ on the surface of the electrolyte layer (E). The thickness of the oxygen electrode layer was 20 - 30 pm before sintering.
- Example 5 Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
- Example 6 Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
- a solid oxide cell was manufactured as Example 1 , with the exception that in step 6 the oxygen electrode layer was prepared by spraying.
- Example 7 Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
- a solid oxide cell was manufactured as Example 3, with the exception that in step 7 Fe- sulfate was used instead of Fe nitrate to prepare the aqueous solution for impregnation.
- Example 8 Preparation of a solid oxide cell with Ce enriched at the oxygen electrode - electrolyte interface
- a solid oxide cell was manufactured as Example 1 , with the exception that in step 4 the slurry of E2 layer comprised TZ8Y + 2 cat.% Ce oxide.
- Symmetrical cell tests The performance and durability of the obtained symmetrical cells were tested at 750°C in air for periods up to 200 hours. The tests were carried out under open circuit voltage condition with periodical impedance measurements. The serial and polarization resistance were deduced from the impedance data and are presented in Figures 3 and 4. The evaluated degradation rates are listed in Table 2 below. As shown in Figure 3, for all the doped samples, further doping YSZ increased the serial resistance. The serial resistance Rs degradation rate was decreased slightly by doping Ce and increased by doping Fe or Mn. For the polarization resistance Rp, Ce and Fe doped samples had both lower initial Rp and lower Rp degradation rate. Mn doping increased the initial Rp, but the Rp degradation rate is smaller than the reference sample.
- Table 2 Degradation rates for the measured serial and polarization resistance. The degradation rate was evaluated based on the measurements in the time period from 140 to 180 h.
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Abstract
The present invention provides various methods of producing a solid oxide cell with an enhanced durability. Dopants are provided at the interface of the electrode comprising LSM and electrolyte and prevent especially the diffusion of Mn from the electrode layer into the electrolyte, stabilizing the LSM and thereby preventing the formation of unwanted degradation products.
Description
Solid oxide cell oxygen electrode with enhanced durability
Technical field The present invention relates to a solid oxide cell with an enhanced durability, and to methods for preparing same.
Background art Solid oxide cells (SOC's) are well known in the art and come in various designs. Typical configurations include a flat plate design and a tubular design, wherein an electrolyte layer is sandwiched between two electrode layers. During operation, usually in a temperature range of from 500°C to 1100°C, one electrode is in contact with oxygen or air and the other electrode is in contact with a fuel gas. Solid oxide cells include solid oxide fuel cells (SOFC's) and solid oxide electrolysis cells (SOEC's).
A 'reversible' solid oxide cell is a cell that can usually consume a fuel gas, such as hydrogen, to produce electricity, and can be reversed so as to consume electricity to produce a gas. Typically, a hydrogen fuel cell, for example, uses hydrogen (H2) and oxygen (02) to produce electricity and water (H20); a reversible hydrogen fuel cell could also use electricity and water to produce hydrogen and oxygen gas. Due to the identical layer design of the cell, the same cell may therefore be in principle used for both applications, and is conseguently referred to as a 'reversible' cell. Several properties are reguired for the SOC's (SOFC's/SOEC's), such as high conductivity, a large area of electrochemically active sites at the electrode/electrolyte interface, chemical and physical stability over a wide range of fuel atmospheres, and minimal mi- crostructural changes with operating time, since such changes are often accompanied by deterioration of electrical performance.
In a solid oxide fuel cell, the oxygen electrode is the cathode where a reduction of oxygen to oxygen ions takes place. In a solid oxide electrolysis cell this electrode is referred to as the anode as here the process is now an oxidation process. A wide range of material properties for SOFC cathodes and SOEC anodes, i.e. the oxygen electrodes of the
respective cell, is required in order to operate the cell with a sufficient life time as demanded by the industry today. Most notably, the oxygen electrodes require high ionic conductivity, high electronic conductivity, good catalytic activity towards oxygen reduction, a thermal expansion coefficient (TEC) that matches the TEC of the other materials of the cell, thermal stability, and chemical stability.
Conventional composite oxygen electrodes are manufactured using an electron conductive material such as lanthanum-strontium-manganite (LSM) and an oxygen ion conductive material such as yttria-stabilized zirconia (YSZ). These electrodes are applied on an electrolyte layer made of an oxygen ion conductive solid oxide, such as YSZ or doped ceria.
In the electrode, the reaction takes place at the so-called triple phase boundaries where electrode material, electrolyte material and the reactive gas are in contact with each other. Efficient gas diffusion and increased contact areas between the electrolyte and the electrodes are therefore important. The performance of the oxygen electrode is mainly determined by the resistance present at the oxygen electrode-electrolyte interface. It is desirable to reduce the interfacial resistance and to increase the number of triple phase boundaries.
The interfacial resistance is for example increased due to degradation products which are formed by a reaction between electrolyte material and electrode material. Examples of such degeneration products include, for example, lanthanum zirconate La2Zr207 (LZO), strontium zirconate (SZO), monoclinic Zr02, or oxides of La-Zr-Si and Sr-Zr-Si. The formation of zirconates (LZO or SZO) or monoclinic zirconia is increased at high temperatures which may occur during the manufacture of the cell when sintering the cell body after formation in its green, i.e. pre-sintered state. The formation of LZO or SZO is also increased during cell testing under high polarization or at high current densities, whereas the formation of monoclinic zirconia is increased with increasing oxygen partial pressure at the interface.
Up to date, the prior art focuses on barrier layers at the interface in between the electrolyte layer and the electrode layer to prevent unwanted side reactions. However, the application of a barrier layer requires one additional step during the manufacture of the cell
and increases the resistance of the cell due to the additional layer itself and due to the additional interface between the barrier layer and the electrolyte layer (which introduces additional interface resistance). Moreover, it has been observed that disadvantageously, diffusion takes place between the barrier layer and the electrolyte layer, and said diffu- sion layer reduces the conductivity of the cell.
EP 2194597 art relates to a solid oxide cell obtainable by a process which comprises the steps of:
- depositing a fuel electrode layer on a fuel electrode support layer
- depositing an electrolyte layer comprising stabilized zirconia on the fuel electrode layer to provide an assembly of fuel electrode support, fuel electrode and electrolyte
- optionally sintering the assembly of fuel electrode support, fuel electrode and electrolyte together to provide a pre-sintered half-cell
- depositing on the electrolyte layer of the pre-sintered half-cell one or more oxygen electrode layers, at least one of the one or more oxygen electrode layers comprising a composite of lanthanum strontium manganite and stabilized zirconia to provide a complete solid oxide cell
- sintering the one or more oxygen electrode layers together with the pre-sintered half-cell to provide a sintered complete solid oxide cell and
- impregnating the one or more oxygen electrode layers of the sintered complete solid oxide cell with manganese to obtain a manganese-impregnated solid oxide cell.
JP 2002/015754 relates to a solid electrolyte fuel cell comprising an air electrode made of a perovskite complex oxide containing at least lanthanum and manganese, a solid electrolyte primarily formed of zirconium oxide, and further a fuel electrode.
US 2006/199057 A1 discloses a solid oxide fuel cell comprising a single cell having an air electrode disposed on a surface of an electrolyte membrane and a fuel electrode disposed on the other surface of the electrolyte membrane, and an interconnector having a role of electrical connection;
wherein the electrolyte membrane is provided with a first layer composed of a material having an oxygen-ionic conductivity of S1 on the air-electrode side, and a second layer composed of a material containing at least zirconia and having an oxygen-ionic conductivity of S2 on the fuel-electrode side; and
wherein the oxygen-ionic conductivity of S1 on the air-electrode side and the oxygen- ionic conductivity of S2 on the fuel-electrode side have a relationship of S1>S2.
Summary
In view of the difficulties of the oxygen electrodes for solid oxide cells suggested in the prior art, it was the object of the present invention to provide an improved oxygen electrode for solid oxide cells with enhanced durability and an improved long term performance, and a method for producing said electrode.
The present invention provides in embodiments a method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming an additional layer on top of said electrolyte layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; or a. l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming a first electrode layer on top of said electrolyte layer;
- forming an additional layer on said electrolyte layer on the side opposite of the first electrode layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
b. l)
- sintering the obtained structure comprising the first electrode layer, the electrolyte layer and the additional layer;
- forming a second electrode layer on top of said additional layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure; or;
a. II)
- forming a first electrode layer; wherein said electrode layer comprises lanthanum strontium manganite;
- forming an additional layer on top of said first electrode layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- forming an electrolyte layer on top of said additional layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b.ll)
- sintering the obtained structure comprising the first electrode layer, the electro- lyte layer and the additional layer;
- forming a second electrode layer on top of said electrolyte layer; and
- sintering the obtained structure.
The present invention further provides a method of producing a solid oxide cell, compris- ing the steps of:
a.1.1)
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; or
a.l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
-forming a first electrode layer on top of said electrolyte layer; and
b)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c)
- applying at least one dopant on top of the electrolyte layer, wherein the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- heat treating the obtained structure;
- forming a second electrode layer on top of the electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
sintering the obtained structure.
The present invention also provides a method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; or
a. l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming a first electrode layer on top of said electrolyte layer; and
b. l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite;
- sintering the obtained structure; or;
a. II)
- forming a first electrode layer; wherein said electrode layer comprises lanthanum strontium manganite;
- forming an electrolyte layer on top of said electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b. ll)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer; and
- sintering the obtained structure; and
c)
- impregnating the electrode layer which comprises lanthanum strontium manganite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- heat treating the cell at a temperature of 300 to 400°C.
The present invention moreover provides a method of producing a solid oxide cell, com¬ prising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
a. l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
-forming a first electrode layer on top of said electrolyte layer; and
b. l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c. l)
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure; or
a.11.1)
- forming a first electrode layer, wherein said electrode layer comprises lanthanum strontium manganite;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
a. ll.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
-forming a first electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
b. II)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
all)
- forming a second electrode layer on top of said electrolyte layer; and
- sintering the obtained structure.
The present invention also provides a solid oxide cell, being obtainable by any of the above methods. Preferred embodiments are set forth in the subclaims and the following detailed description.
Brief description of the drawings Figure 1 relates to a solid oxide cell in accordance with the present invention, where the dopant/dopants are enriched in the region close to the oxygen electrode - electrolyte interface.
Figure 2 illustrates a solid oxide cell in accordance with the present invention, where the yttria stabilized zirconia electrolyte layer is replaced with doped YSZ.
Figure 3 illustrates the serial resistance of the symmetrical cells tested at 750°C in air for periods up to 200 hours. Figure 4 illustrates the polarization resistance of the symmetrical cells tested at 750°C in air for periods up to 200 hours.
Detailed description of the invention - First Embodiment
In the first embodiment, the present invention provides a method of producing a solid oxide cell, wherein an additional layer is formed in between the electrolyte layer and the electrode layer which comprises lanthanum strontium manganite. More specifically, the
present invention provides a method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming an additional layer on top of said electrolyte layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; or a.l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
-forming a first electrode layer on top of said electrolyte layer;
- forming an additional layer on said electrolyte layer on the side opposite of the first electrode layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
b. l)
- sintering the obtained structure comprising the first electrode layer, the electro- lyte layer and the additional layer;
- forming a second electrode layer on top of said additional layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure; or;
a. II)
- forming a first electrode layer; wherein said electrode layer comprises lanthanum strontium manganite;
- forming an additional layer on top of said first electrode layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- forming an electrolyte layer on top of said additional layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b.ll)
- sintering the obtained structure comprising the first electrode layer, the electrolyte layer and the additional layer;
- forming a second electrode layer on top of said electrolyte layer; and
- sintering the obtained structure.
Advantageously, with the method of the present invention, an additional layer is formed on the electrolyte layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant. Said dopants are present at the interface of the electrolyte and electrode and prevent especially the diffusion of Mn from the second electrode layer into the electrolyte, stabilizing the LSM and thereby preventing the formation of unwanted degradation products such as LZO or SZO.
During the sintering step, the additional layer and the electrolyte layer form one layer which from a macroscopic point of view appears to be an electrolyte layer with the dopant enriched on one surface thereof rather than a separate barrier layer on top of the electrolyte layer. Unlike the barrier layers suggested in the prior art, which form a distinct and separate layer, the present invention therefore provides an improved structure which prevents diffusion especially of Mn from the electrode layer into the electrolyte layer at the interface where the dopant is enriched. The so obtained improved structure reduces or avoids the increased internal resistance and conductivity losses which occurs in case of a separate barrier layer as proposed in the prior art.
Instead, the dopant provided with the additional layer is capable to stabilize the LSM- YSZ interface and prevents unwanted reactions between the electrode material and electrolyte material without the disadvantages of diffusion and without the additional increased internal resistance and conductivity losses.
The cell may be produced by using the first formed layer as a support layer. Usually, this layer is relatively thick, as compared to the other layers, to provide additional mechanical support. Alternatively, if desired, an additional support may be used if desired, on which the first layer is applied. The first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layers.
In one preferred embodiment, the first electrode layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is
used. In this embodiment, and independent of the use of an additional support, the method comprises the steps of:
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming an additional layer on top of said electrolyte layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- sintering the obtained structure comprising the first electrode layer, the electrolyte layer and the additional layer;
- forming a second electrode layer on top of said additional layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure.
After sintering, the additional layer and the electrolyte layer form the specific structure as outlined above, i.e. in the electrolyte structure, the dopant is enriched on the surface opposite the electrolyte layer surface in contact with the first electrode layer. On the surface with the enriched dopant, the second electrode layer, which comprises lanthanum strontium manganite, is applied. The dopant effectively reduces or suppresses the Mn diffusion from the electrode layer which comprises lanthanum strontium manganite into the electrolyte layer.
In another preferred embodiment, the electrolyte layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used. In this embodiment, and independent of the use of an additional support, the method comprises the steps of:
a.1.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
-forming a first electrode layer on top of said electrolyte layer;
- forming an additional layer on said electrolyte layer on the side opposite of the first electrode layer, wherein the additional layer comprises yttria stabilized zirco- nia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
b.l)
- sintering the obtained structure comprising the first electrode layer, the electrolyte layer and the additional layer;
- forming a second electrode layer on top of said additional layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure.
In yet another preferred embodiment, the electrode layer which comprises lanthanum strontium manganite is the first formed layer which preferably functions as the support layer for all other layers if no additional support is used. In this case, the additional layer has to be applied on said layer first, followed by the formation of the electrolyte layer, so as to provide a dopant enriched surface of the electrolyte at the interface to the electrode comprising lanthanum strontium manganite. In this case, the method comprises the steps of:
a. II)
- forming a first electrode layer; wherein said electrode layer comprises lanthanum strontium manganite;
- forming an additional layer on top of said first electrode layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- forming an electrolyte layer on top of said additional layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b. ll)
- sintering the obtained structure comprising the first electrode layer, the electrolyte layer and the additional layer;
- forming a second electrode layer on top of said electrolyte layer; and
- sintering the obtained structure.
The dopants are generally selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y. Preferred dopants are oxides of Fe, Mg or Ce, more preferably Fe or
Mg. The most preferred dopant is Fe. Further preferred is the amount of dopants being in the range of 0.1 - 10 cat.% (cation percentage), preferably in the range of 0.3 - 5 cat.% and more preferably in the range of 0.5 - 2 cat.%. The cation percentage is based on all metal elements but excludes oxygen.
In order to keep the resistance of the cell and the additional material needed for the additional layer at a minimum, the additional layer on the electrolyte layer is as thin as possible. The additional layer has preferably a thickness of 5 pm or less, and more preferably a thickness of 2 pm or less.
The electrode which comprises lanthanum strontium manganite further preferably comprises yttria stabilized zirconia, and even more preferably comprises yttria stabilized zir- conia and a dopant. Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y. Second Embodiment
In the method of the second embodiment, the dopant is directly applied on top of the electrolyte layer instead of being part of an additional layer. Advantageously, in this embodiment the formation of the additional layer prior to sintering can be omitted, thereby being more cost effective due to less material being used. More specifically, the present invention provides a method of producing a solid oxide cell, comprising the steps of: a.1.1)
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; or
a.l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
-forming a first electrode layer on top of said electrolyte layer; and
b)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c)
- applying at least one dopant on top of the electrolyte layer, wherein the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- heat treating the obtained structure;
- forming a second electrode layer on top of the electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure.
As outlined above for the first embodiment, the cell may be produced by using the first layer as a support layer. Usually, this layer is relatively thick, as compared to the other layers, to provide mechanical support. Alternatively, if desired, an additional support may be used if desired, on which the first layer is applied.
In one preferred embodiment, the first electrode layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used. In this embodiment, and independent of the use of an additional support, the method comprises the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c)
- applying at least one dopant on top of the electrolyte layer, wherein the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- heat treating the obtained structure;
- forming a second electrode layer on top of the electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure.
Alternatively, the electrolyte layer is the first formed layer which preferably functions as the support layer for all other layers if no additional support is used. In this case, the method comprises the steps of
a.1.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
-forming a first electrode layer on top of said electrolyte layer; and
b)
- sintering the obtained structure comprising the first electrode layer and the elec- trolyte layer;
c)
- applying at least one dopant on top of the electrolyte layer, wherein the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- heat treating the obtained structure;
- forming a second electrode layer on top of the electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure. In this embodiment, the dopant is directly applied on top of the electrolyte layer instead of being part of an additional layer. Advantageously, in this embodiment the formation of the additional layer can be omitted, thereby being more cost effective due to less material and one production step less. Preferably, the dopant is applied by a method such as screen printing, spraying or spin coating. The dopant is selected form the group consist- ing of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y. Preferred dopants are oxides of Ce, Mg or Fe, more preferably Fe or Mg. The most preferred dopant is Fe.
After application of the dopant, a heat treatment step is carried out. The heat treatment step is preferably carried out at a temperature of from 600 to 1250°C, more preferably at a temperature of from 600 to 1000°C, more preferably of from 650 to 900°C, and even more preferably at a temperature of from 700 to 850°C.
The electrode which comprises lanthanum strontium manganite preferably comprises yttria stabilized zirconia, and even more preferably comprises yttria stabilized zirconia and a dopant. Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y. - Third embodiment
In the method of the third embodiment, the second electrode layer which comprises lanthanum strontium manganite is impregnated with at least one dopant after the sintering step. More specifically, the present invention provides a method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; or
a.l.2))
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming a first electrode layer on top of said electrolyte layer; and
b. l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite;
- sintering the obtained structure; or;
a. II)
- forming a first electrode layer; wherein said electrode layer comprises lanthanum strontium manganite;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b.ll)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer; and sintering the obtained structure; and
- impregnating the electrode layer which comprises lanthanum strontium man- ganite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- heat treating the cell at a temperature of 300 to 400°C.
As outlined above for the first embodiment, the cell may be produced by using the first layer as a support layer. Alternatively, if desired, an additional support may be used if desired, on which the first layer is applied. The first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layers.
In one preferred embodiment, the first electrode layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used. In this embodiment, and independent of the use of an additional support, the method comprises the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b.l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite;
- sintering the obtained structure;
c)
- impregnating the electrode layer which comprises lanthanum strontium manganite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- heat treating the cell at a temperature of 300 to 400°C.
In another preferred embodiment, the electrolyte layer is the first formed layer which preferably functions as the support layer for all other layers if no additional support is
used, independent of the use of an additional support, the method comprises the steps of:
a.1.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming a first electrode layer on top of said electrolyte layer; and
b.l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite;
- sintering the obtained structure;
c)
- impregnating the electrode layer which comprises lanthanum strontium mangan- ite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- heat treating the cell at a temperature of 300 to 400°C.
In a further preferred embodiment, the second electrode layer comprises lanthanum strontium manganite forms the first layer which preferably functions as the support layer for all other layers if no additional support is used. Independent of the use of an additional support, the method comprises the steps of:
a. II)
- forming a first electrode layer; wherein said electrode layer comprises lantha- num strontium manganite;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
b. ll)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer; and sintering the obtained structure; and
c)
- impregnating the electrode layer which comprises lanthanum strontium mangan- ite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- heat treating the cell at a temperature of 300 to 400°C.
In the third embodiment, the second electrode layer is impregnated with at least one dopant after the sintering step. This allows for a production of the cell without the need of applying an extra layer with the dopant, which is only added after the sintering step, followed by a heat treatment. In this embodiment, the dopant can advantageously be employed in form of a solution suitable for impregnation of the electrode.
Preferably, the dopant impregnated into the second electrode layer is in form of a nitrate, sulphate or chloride of Ca, Ce, Fe, Gd, Mg, Sm and Y. More preferred are dopants of Fe, Mg or Ce in form of a nitrate, sulphate or chloride, even more preferably dopants of Fe or Mg in form of a nitrate, sulphate or chloride. The most preferred dopant is Fe in form of a nitrate, sulphate, or chloride.
The impregnation of the electrode can be carried out in one step. Alternatively, the impregnation can be repeatedly carried out until a predetermined amount of dopant is achieved.
In another preferred embodiment, the electrode which comprises lanthanum strontium manganite further comprises yttria stabilized zirconia and even more preferably comprises yttria stabilized zirconia and a dopant. Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y.
Fourth embodiment
In the Fourth embodiment, the present invention provides a method of producing a solid oxide cell, wherein the dopant is already comprised in the electrolyte layer. Thus, additional steps such as the application of an additional layer or the impregnation of the second electrode layer are not necessary. More specifically, the present invention provides a method of producing a solid oxide cell, comprising the steps of:
a.1.1)
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
a.1.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
-forming a first electrode layer on top of said electrolyte layer; and
b. l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c. l)
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure; or
a.11.1 )
- forming a first electrode layer, wherein said electrode layer comprises lanthanum strontium manganite;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
a. ll.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
-forming a first electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
b. ll)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c. ll)
- forming a second electrode layer on top of said electrolyte layer; and - sintering the obtained structure.
As outlined in detail for the first embodiment, the first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layer.
The cell may be produced by using the first layer as a support layer. Usually, this layer is relatively thick, as compared to the other layers, to provide mechanical support. Alternatively, if desired, an additional support may be used if desired, on which the first layer is applied. The first layer being preferably used as a support layer may either be one of the electrode layers or the electrolyte layers.
In one preferred embodiment, the first electrode layer is the first layer being formed, which preferably functions as the support layer for all other layers if no additional support is used. Independent of the use of an additional support, the method comprises the steps of:
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of
Ca, Ce, Fe, Gd, Mg and Sm;
and
b. l)
- sintering the obtained structure comprising the first electrode layer and the elec- trolyte layer;
c. l)
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure.
In another preferred embodiment, the electrolyte layer is the first formed layer, which preferably functions as the support layer for all other layers if no additional support is used. Independent of the use of an additional support, the method comprises the steps of:
a.1.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
-forming a first electrode layer on top of said electrolyte layer; and
b.l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c.l)
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure.
In a further preferred embodiment, the electrode layer which comprises lanthanum stron- tium manganite forms the first layer which preferably functions as the support layer for all other layers if no additional support is used. Independent of the use of an additional support, the method comprises the steps of:
a.11.1 )
- forming a first electrode layer, wherein said electrode layer comprises lantha- num strontium manganite;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
a.ll.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
- forming a first electrode layer on top of said electrolyte layer, wherein said elec- trode layer comprises lanthanum strontium manganite; and
b.ll)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
al l)
- forming a second electrode layer on top of said electrolyte layer; and
- sintering the obtained structure.
In the fourth embodiment, the dopant is already comprised in the electrolyte layer. Thus, additional steps such as the application of an additional layer or the impregnation of the second electrode layer are not necessary. However, the amount of dopant has to be increased so as to ensure that in the composition, the amount of dopant present on the interface is still sufficient to suppress any unwanted reactions. Preferred dopants are oxides of Fe, Mg or Ce, more preferably Fe or Mg. The most preferred dopant is Fe.
The electrode which comprises lanthanum strontium manganite further preferably comprises yttria stabilized zirconia, and even more preferably comprises yttria stabilized zir- conia and a dopant. Suitable dopants are oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y. In all methods as outlined above, the sintering step is preferably carried out at a temperature of from 1000°C and 1500°C, more preferably at a temperature of from 1 100 to 1450°C.
In the second electrode layer of all embodiments, the composition preferably comprises a composite of LSM and stabilized zirconia. Further preferred is the atomic ratio of manganese to lanthanum and strontium in the LSM being greater than 1 , more preferably being greater than 1 .02. Stabilized zirconia can be yttria, or MgO, or CaO stabilized zirconia or any other material known in the art. The thickness of the electrolyte layer in all embodiments is generally in the range of from 1 to 200 μητι, preferably from 5 to 150 pm, and more preferably of from 10 to 100 pm. If the electrolyte layer however functions as a support layer, the thickness is preferably in the range of from 30 to 200 pm, preferably from 50 to 150 pm, and more preferably of from 60 to 100 pm.
The thickness of each electrode layer in all embodiments is generally in the range of from 5 to 200 pm, preferably from 10 to 150 pm, and more preferably of from 20 to 100 pm. If the respective electrode layer however functions as a support layer, the thickness
is preferably in the range of from 30 to 200 pm, preferably from 50 to 150 pm, and more preferably of from 60 to 100 pm.
The present invention also provides a solid oxide cell, being obtainable by the above methods. The solid oxide cell can be used as a solid oxide fuel cell or a solid oxide electrolysis cell.
The material for the fuel electrode layer can be any material known in the art for a fuel electrode. For instance, a Ni-stabilized zirconia composite may be used. Alternatively, the layer may comprise metal alloy particles, such as Fe-Cr alloy particles. If desired, the cell may further comprise additional layers, such as a support layer.
Advantageously, with the methods of the present invention, reactions in between LSM of the electrode and YSZ of the electrolyte at the interface can effectively be reduced or prevented, and the formation of especially, zirconates such as LZO, SZO, La-Zr-Si and Sr-Zr-Si is suppressed, due to the presence of a dopant at the interface. The dopant ensures that especially the amount of Mn in the electrode is maintained at thus the LSM is stabilized. This results in a reduction of degradation in the SOC (SOFC/SOEC) and an increase in the performance and overall life time of the cell.
Additionally, the adhesion between the oxygen electrode and the electrolyte of the solid oxide cell is improved because LSM grains are prevented from detaching themselves from the stabilized zirconia electrolyte surface. In the following, the present invention will be further illustrated with reference to detailed examples. The invention is however not restricted thereto.
Examples Powder reaction study
Pellets were made from a powder mixture of Yo.-i5Zro.85O1.925 : Lao.75Sro.25Mn-i.05O3 : MOx = 2:1 :0.1 (molar ratio), in which M represents Ca, Ce, Fe, Mg, Mn, Y. Also reference pellets were prepared by mixing YSZ with LSM (Yo.15 ro.e5O1.925 : Lao.75 ro.25Mn1.05O3 = 2:1).
The pellets were annealed at 1000°C in N2 or in air for 8 weeks and were examined by XRD to detect possible reaction products.
Table 1 : XRD-detected secondary phases formed in the above pellets. The numbers in parentheses are the intensity ratios between the secondary phases and the cubic YSZ phase.
As shown in Table 1 , both La2Zr207 and SrZr03 were detected as reaction products for the samples annealed in N2, and m-Zr02 was detected as a reaction product for the samples annealed in air, though the amount of these reaction products vary from sample to sample. Both Ce and Fe oxides showed a strong effect in preventing the zirconate formation, as illustrated by the much lower intensity of La2Zr207 and SrZr03 as compared to the reference sample, while Ca, Ce, Mg and Y oxides were effective in preventing the m-Zr02 formation.
Example 1 : Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface A solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
1 ) tape-casting a fuel electrode support layer (AS);
2) tape-casting a fuel electrode layer (A) on the surface of the fuel electrode support layer;
3) tape-casting a 8 pm first electrolyte layer (E1) of 8 mol% Y203-stabilised zirconia (TZ8Y) on the surface of the fuel electrode layer;
4) tape-casting a 2 pm second electrolyte layer (E2) of TZ8Y+2 cat.% Fe oxide on the surface of the first electrolyte layer to obtain a half cell;
5) sintering the half cell at a temperature above 1200°C. After sintering, the E1 and E2 layer will become one electrolyte layer (E), with no interface between E1 and E2;
6) screen printing a LSM-YSZ oxygen electrode layer (C) of 20-30 pm in thickness on the surface of the electrolyte layer;
7) simultaneously sintering the half cell and the LSM-YSZ oxygen electrode layer deposited on the half cell.
The following details refer to the preparation steps of example 1 :
The suspension for tape-casting is manufactured by means of ball milling of powders with polyvinyl pyrrolidone (PVP), polyvinyl butyral (PVB) and ethanol (EtOH) and methyl ethyl ketone (MEK) as additives. The suspension is tape-cast using a double blade setup and the tape is subsequently dried.
1 ) AS layer: The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder. The green thickness of the tape-cast layer was in the range of 400 pm. The porosity of this layer was in the range of 30% after sintering and reduction.
2) A layer: The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was approximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
3) E1 layer: The slurry of E1 layer comprised TZ8Y.
4) E2 layer: The slurry of E2 layer comprised TZ8Y + 2 cat.% Fe oxide. After tape casting and sintering E1 and E2 layer will become one electrolyte layer (E), with no interface between E1 and E2. The thickness of the E layer was approximately 10 pm.
5) The half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100°C/h and left for about 12 hours and to cool to room temperature to form a sintered half cell. After sintering, the electrolyte layer was enriched with Fe close to the surface where the oxygen electrode will be applied.
6) An oxygen electrode layer was deposited on the sintered half cell by screen printing an ink comprising a 1 :1 weight ratio mixture of
and YSZ on the surface of the electrolyte layer (E). The thickness of the oxygen electrode layer was 20 - 30 μητι before sintering.
7) Sintering the half cell deposited with an oxygen electrode layer in a furnace at approximately 1 100°C for 2 hours and then cooling down to room temperature.
Example 2: Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
A solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
1 ) tape-casting a fuel electrode support layer (AS);
2) tape-casting a fuel electrode layer (A) on the surface of the fuel electrode support layer;
3) tape-casting a 10 μιτι electrolyte layer (E) of 8 mol% Y203-stabilised zirconia (TZ8Y) on the surface of the fuel electrode layer;
4) sintering the half cell at a temperature above 1200°C;
5) spin coating a 0.2 pm Fe oxide layer on the surface of the electrolyte layer:
6) heat treating the obtained structure at a temperature around 1000°C to allow Fe diffuse into the electrolyte layer.
7) screen printing a LSM-YSZ oxygen electrode layer (C) of 20-30 pm in thickness on the surface of the electrolyte layer;
8) simultaneously sintering the half cell and the LSM-YSZ oxygen electrode layer deposited on the half cell.
The following details refer to the preparation steps of example 2:
1 ) AS layer: The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder. The green thickness of the tape-cast layer was in the range of 400 pm. The porosity of this layer was in the range of 30% after sintering and reduction.
2) A layer: The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was ap-
proximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
3) E layer: The slurry of E layer comprised TZ8Y. After tape casting and sintering the thickness of the E layer was approximately 10 pm.
4) The half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100°c/h and left for about 12 hours and to cool to room temperature to form a sintered half cell.
5) Spin coating a 0.2 pm Fe oxide layer on the surface of the electrolyte layer.
6) Heat treating the obtained structure at a temperature around 1000°C for about 10 hours to allow Fe diffuse into the electrolyte layer. The undissolved Fe oxide can be removed by polishing the electrolyte surface using SiC paper grade No. 1200.
7) An oxygen electrode layer was deposited on the sintered half cell by screen printing an ink comprising a 1 :1 weight ratio mixture of Lao /sSro^sMnLosC^ and YSZ on the surface of the electrolyte layer (E). The thickness of the oxygen electrode layer was 20 - 30 pm before sintering.
8) Sintering the half cell deposited with an oxygen electrode layer in a furnace at approximately 1100°C for 2 hours and then cooling down to room temperature.
Example 3: Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
A solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
1 ) tape-casting a fuel electrode support layer (AS);
2) tape-casting a fuel electrode layer (A) on the surface of the fuel electrode support layer;
3) tape-casting a 10 pm electrolyte layer (E) of TZ8Y on the surface of the fuel electrode layer;
4) sintering the half cell at a temperature above 1200°C;
5) screen printing a LSM-YSZ oxygen electrode layer (C) of 20-30 pm in thickness on the surface of the electrolyte layer;
6) simultaneously sintering the half cell and the LSM-YSZ oxygen electrode layer deposited on the half cell.
7) impregnating the oxygen electrode with Fe-Nitrate aqueous solution prepared by dissolving 10 g Fe-nitrate in 100 ml distilled water. Repeating the impregnation step until a concentration of 0.5-5 mg Fe/cm2 is obtained in the impregnated cell.
8) heating the impregnated cell at a temperature of 350°C for 2 hours to decompose the nitrate into oxide.
The following details refer to the preparation steps of example 3:
1 ) AS layer: The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder. The green thickness of the tape-cast layer was in the range of 400 pm. The porosity of this layer was in the range of 30% after sintering and reduction.
2) A layer: The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was approximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
3) E layer: The slurry of E layer comprised TZ8Y. After tape casting and sintering the thickness of the E layer was approximately 10 pm.
4) The half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100°c/h and left for about 12 hours and to cool to room temperature to form a sintered half cell.
5) An oxygen electrode layer was deposited on the sintered half cell by screen printing an ink comprising a 1 :1 weight ratio mixture of Lao ysSro asMn-i osO^ and YSZ on the surface of the electrolyte layer (E). The thickness of the oxygen electrode layer was 20 - 30 pm before sintering.
6) Sintering the half cell deposited with an oxygen electrode layer in a furnace at approximately 1100°C for 2 hours and then cooling down to room temperature.
7) Impregnating the oxygen electrode layer with Fe: A Fe-Nitrate aqueous solution was made by dissolving 10 g Fe-Nitrate (purity 99.999%) in 100 ml distilled water. The solution was dripped on the surface of the porous oxygen electrode layer by an eye dropper. The impregnation process was repeated at least twice to supply a concentration of 0.5-5 mg Fe/cm2 on the oxygen electrode surface to obtain a solid oxide cell.
8) Heating the impregnated cell at a temperature of 350°C for 2 hours to decompose the nitrate into oxide.
Example 4: Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
A solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface is manufactured by the following steps:
1 ) tape-casting a fuel electrode support layer (AS);
2) tape-casting a fuel electrode layer (A) on the surface of the fuel electrode support layer;
3) tape-casting a 10 pm electrolyte layer (E) of TZ8Y + 2 cat.% Fe oxide on the surface of the fuel electrode layer;
4) sintering the half cell at a temperature above 1200°C;
5) screen printing a LSM-YSZ oxygen electrode layer (C) of 20-30 pm in thickness on the surface of the electrolyte layer;
6) simultaneously sintering the half cell and the LSM-YSZ oxygen electrode layer deposited on the half cell.
The following details refer to the preparation steps of example 4:
1 ) AS layer: The suspension comprised 45% yttria stabilised zirconia (YSZ) and 55 vol% NiO powder. The green thickness of the tape-cast layer was in the range of 400 pm. The porosity of this layer was in the range of 30% after sintering and reduction.
2) A layer: The slurry of A layer comprised 40 vol% YSZ and about 60 vol% NiO powder. After tape casting and sintering the thickness of the A-layer was approximately 10 pm. The porosity of this layer was approximately 25% after sintering and reduction.
3) E layer: The slurry of E layer comprised TZ8Y + 2 cat.% Fe oxide. After tape casting and sintering the thickness of the E layer was approximately 10 pm.
4) The half cell consisting of the fuel electrode support layer, the fuel electrode layer and the electrolyte layer was sintered in a furnace at a temperature above 1200°C with a ramp up of 100°c/h and left for about 12 hours and to cool to room temperature to form a sintered half cell.
5) An oxygen electrode layer was deposited on the sintered half cell by screen print¬ ing an ink comprising a 1 :1 weight ratio mixture of
and YSZ on the surface of the electrolyte layer (E). The thickness of the oxygen electrode layer was 20 - 30 pm before sintering.
6) Sintering the half cell deposited with an oxygen electrode layer in a furnace at approximately 1 100°C for 2 hours and then cooling down to room temperature.
Example 5: Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
A solid oxide cell was manufactured as Example 1 , with the exception that in steps 2, 3 and 4, the fuel electrode layer (A) and the electrolyte layers (E1 and E2) were prepared by spraying. Example 6: Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
A solid oxide cell was manufactured as Example 1 , with the exception that in step 6 the oxygen electrode layer was prepared by spraying.
Example 7: Preparation of a solid oxide cell with Fe enriched at the oxygen electrode - electrolyte interface
A solid oxide cell was manufactured as Example 3, with the exception that in step 7 Fe- sulfate was used instead of Fe nitrate to prepare the aqueous solution for impregnation.
Example 8: Preparation of a solid oxide cell with Ce enriched at the oxygen electrode - electrolyte interface A solid oxide cell was manufactured as Example 1 , with the exception that in step 4 the slurry of E2 layer comprised TZ8Y + 2 cat.% Ce oxide.
Symmetrical cell tests:
The performance and durability of the obtained symmetrical cells were tested at 750°C in air for periods up to 200 hours. The tests were carried out under open circuit voltage condition with periodical impedance measurements. The serial and polarization resistance were deduced from the impedance data and are presented in Figures 3 and 4. The evaluated degradation rates are listed in Table 2 below. As shown in Figure 3, for all the doped samples, further doping YSZ increased the serial resistance. The serial resistance Rs degradation rate was decreased slightly by doping Ce and increased by doping Fe or Mn. For the polarization resistance Rp, Ce and Fe doped samples had both lower initial Rp and lower Rp degradation rate. Mn doping increased the initial Rp, but the Rp degradation rate is smaller than the reference sample.
Table 2: Degradation rates for the measured serial and polarization resistance. The degradation rate was evaluated based on the measurements in the time period from 140 to 180 h.
In the symmetrical cell tests, Ce and Fe again showed a positive effect in decreasing both the initial Rp and the long term Rp degradation rate. The adverse effect of increasing initial Rs can probably be minimized by carefully tailoring the concentration and distribution of Ce and Fe in YSZ, i.e. with minimum concentration of Ce and Fe enriched at the LSM-YSZ interface.
Claims
1 . A method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming an additional layer on top of said electrolyte layer, wherein the addi- tional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; or a.l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
-forming a first electrode layer on top of said electrolyte layer;
- forming an additional layer on said electrolyte layer on the side opposite of the first electrode layer, wherein the additional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
b.l)
sintering the obtained structure comprising the first electrode layer, the electrolyte layer and the additional layer;
- forming a second electrode layer on top of said additional layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure; or;
a. II)
- forming a first electrode layer; wherein said electrode layer comprises lanthanum strontium manganite;
- forming an additional layer on top of said first electrode layer, wherein the addi- tional layer comprises yttria stabilized zirconia and at least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- forming an electrolyte layer on top of said additional layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b. ll)
- sintering the obtained structure comprising the first electrode layer, the electrolyte layer and the additional layer;
- forming a second electrode layer on top of said electrolyte layer; and
sintering the obtained structure.
2. The method of claim 1 , wherein the dopant for the electrolyte layer is an oxide of Ce, Fe or Mg.
3. The method of claim 1 or 2, wherein the additional layer on the electrolyte layer has a thickness of 2 pm or less.
4. A method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; or
a.l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
-forming a first electrode layer on top of said electrolyte layer; and
b)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c)
- applying at least one dopant on top of the electrolyte layer, wherein the least one dopant selected from the group consisting of oxides of Ca, Ce, Fe, Gd, Mg, Sm and Y;
- heat treating the obtained structure;
- forming a second electrode layer on top of the electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure.
5. The method of claim 4, wherein the dopant is applied by screen printing, spraying or spin coating.
6. The method of claim 4 or 5, wherein the heat treatment step is carried out at a temperature of from 600 to 1000°C.
7. The method of any one of claims 4 to 6, wherein the applied dopant is an oxide of Ce, Fe or Mg.
8. The method of any one of claims 1 to 7, wherein the electrode which comprises lanthanum strontium manganite further comprises yttria stabilized zirconia and a dopant.
9. A method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; or
a.l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia;
- forming a first electrode layer on top of said electrolyte layer; and
b.l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite;
- sintering the obtained structure; or;
- forming a first electrode layer; wherein said electrode layer comprises lanthanum strontium manganite;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia; and
b.ll)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
- forming a second electrode layer on top of said electrolyte layer; and
- sintering the obtained structure; and
c)
- impregnating the electrode layer which comprises lanthanum strontium mangan- ite with at least one dopant, wherein the least one dopant is selected from the group consisting of Ca, Ce, Fe, Gd, Mg, Sm and Y; and
- heat treating the cell at a temperature of 300 to 400°C.
10. The method of claim 9, wherein the dopant impregnated into the second electrode layer is in form of a nitrate, sulphate or chloride of Ca, Ce, Fe, Gd, Mg, Sm and Y.
1 1. The method of claim 9 or 10, wherein the electrode which comprises lanthanum strontium manganite further comprises yttria stabilized zirconia and a dopant.
12. A method of producing a solid oxide cell, comprising the steps of:
a.1.1 )
- forming a first electrode layer;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm; or
a. l.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
-forming a first electrode layer on top of said electrolyte layer; and
b. l)
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
c. l)
- forming a second electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure; or
a.11.1 )
- forming a first electrode layer, wherein said electrode layer comprises lanthanum strontium manganite;
- forming an electrolyte layer on top of said first electrode layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of
Ca, Ce, Fe, Gd, Mg and Sm; or
a.11.2)
- forming an electrolyte layer, wherein said electrolyte layer comprises yttria stabilized zirconia and at least one dopant, wherein the least one dopant selected from the group consisting of an oxide of Ca, Ce, Fe, Gd, Mg and Sm;
-forming a first electrode layer on top of said electrolyte layer, wherein said electrode layer comprises lanthanum strontium manganite; and
- sintering the obtained structure comprising the first electrode layer and the electrolyte layer;
al l)
forming a second electrode layer on top of said electrolyte layer; and
sintering the obtained structure.
13. The method of claim 12, wherein the electrode which comprises lanthanum strontium manganite further comprises yttria stabilized zirconia and a dopant.
14. The method of any one of claims 1 to 13, wherein the sintering step is carried out at a temperature of from 1000°C and 1500C°C.
15. A solid oxide cell, being obtainable by the method of any one of claims 1 to 14.
16. Use of the solid oxide cell of claim 15 as a solid oxide fuel cell or a solid oxide electrolysis cell.
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| EP12005300.4 | 2012-07-19 |
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