WO2015197767A1 - Anode support creep - Google Patents

Anode support creep Download PDF

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Publication number
WO2015197767A1
WO2015197767A1 PCT/EP2015/064392 EP2015064392W WO2015197767A1 WO 2015197767 A1 WO2015197767 A1 WO 2015197767A1 EP 2015064392 W EP2015064392 W EP 2015064392W WO 2015197767 A1 WO2015197767 A1 WO 2015197767A1
Authority
WO
WIPO (PCT)
Prior art keywords
solid oxide
process according
oxide cell
reduction
temperature
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/EP2015/064392
Other languages
French (fr)
Inventor
Thomas Heiredal-Clausen
Henrik Lund Frandsen
Thomas Karl Petersen
Mads Find Madsen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Topsoe AS
Original Assignee
Haldor Topsoe AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Haldor Topsoe AS filed Critical Haldor Topsoe AS
Priority to EA201790090A priority Critical patent/EA201790090A1/en
Priority to CN201580034136.7A priority patent/CN106463747B/en
Priority to KR1020177000148A priority patent/KR20170023929A/en
Priority to AU2015279216A priority patent/AU2015279216B2/en
Priority to CA2952338A priority patent/CA2952338C/en
Priority to JP2016574222A priority patent/JP6894705B2/en
Priority to US15/321,641 priority patent/US20170214061A1/en
Publication of WO2015197767A1 publication Critical patent/WO2015197767A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/70—Assemblies comprising two or more cells
    • C25B9/73—Assemblies comprising two or more cells of the filter-press type
    • C25B9/77—Assemblies comprising two or more cells of the filter-press type having diaphragms
    • 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
    • H01M8/1213—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte characterised by the electrode/electrolyte combination or the supporting material
    • 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
    • H01M2008/1293—Fuel cells with solid oxide electrolytes
    • 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
    • H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
    • H01M4/8652—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites as mixture
    • 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
    • H01M4/9041—Metals or alloys
    • H01M4/905—Metals or alloys specially used in fuel cell operating at high temperature, e.g. SOFC
    • H01M4/9066—Metals or alloys specially used in fuel cell operating at high temperature, e.g. SOFC of metal-ceramic composites or mixtures, e.g. cermets
    • 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 invention relates to a production process for a solid oxide cell (SOC) , in particular a solid oxide fuel cell (SOFC) stack system or a solid oxide electrolysis cell (SOEC) stack system.
  • SOC solid oxide cell
  • SOFC solid oxide fuel cell
  • SOEC solid oxide electrolysis cell
  • the invention concerns a process to control the anode support creep during reduction to control thermo-mechanical stress in cells in SOC stacks.
  • a Solid Oxide Fuel Cell comprises a solid electro- lyte that enables the conduction of oxygen ions, a cathode where oxygen is reduced to oxygen ions and an anode where hydrogen is oxidised.
  • the overall reaction in an SOFC is that hydrogen and oxygen electrochemically react to produce electricity, heat and water.
  • the anode normally possesses catalytic ac ⁇ tivity for the steam reforming of hydrocarbons, particularly natural gas, whereby hydrogen, carbon dioxide and carbon monoxide are generated. Reforming of methane, the main com ⁇ ponent of natural gas, can be described by the following reactions:
  • an oxidant such as air is supplied to the solid oxide fuel cell in the cathode region.
  • Fuel such as hydrogen is supplied in the anode region of the fuel cell.
  • a hydrocarbon fuel such as methane is sup ⁇ plied in the anode region, where it is converted to hydro ⁇ gen and carbon oxides by the above reactions.
  • Hydrogen passes through the porous anode and reacts at the anode/- electrolyte interface with oxygen ions generated on the cathode side that have diffused through the electrolyte. Oxygen ions are created in the cathode side with an input of electrons from the external electrical circuit of the cell.
  • interconnects To increase voltage, several cell units are assembled to form a stack and are linked together by interconnects.
  • ⁇ terconnects normally serve as a gas barrier to separate the anode (fuel) and cathode (air/oxygen) sides of adjacent cell units, and at the same time they enable current con ⁇ duction between the adjacent cells, i.e. between an anode of one cell with a surplus of electrons and a cathode of a neighbouring cell needing electrons for the reduction pro- cess.
  • interconnects are normally provided with a plurality of flow paths for the passage of fuel gas on one side of the interconnect and oxidant gas on the opposite side .
  • the way the anode and cathode gas flows are distributed in an SOFC stack is by having a common manifold for each of the two process gasses.
  • the manifolds can either be inter- nal or external.
  • the manifolds supply process gasses to the individual layers in the SOFC stack by the means of chan ⁇ nels to each layer.
  • the channels are normally situated in one layer of the repeating elements which are comprised in the SOFC stack, i.e. in the spacers or in the interconnect.
  • the SOC is a combination of several layers all with differ ⁇ ent Thermal Expansion Coefficients (TEC) .
  • TEC Thermal Expansion Coefficients
  • the Anode Support will contract more than the electrolyte during cooling from the 1200°C, and thereby put the electrolyte in compression .
  • the reason for putting the thin electrolyte under compres ⁇ sion by the Anode Support is that the thin layer will frac ⁇ ture easily if it is under tension, whereas the thick Anode Support can handle the tension better.
  • the electrolyte will be in compression for all temperatures below the sintering temperature, but will be in tension at temperatures above the sintering temperature.
  • the Anode Support comprises a cer ⁇ met of NiO and YSZ.
  • the NiO has to be reduced into Ni . This reduction of the SOC is done after assembly and conditioning of the SOC stack at a temperature above 500 °C - the reduction tempera ⁇ ture .
  • the operation temperature of the SOC stack compared to the reduction temperature is thus an important parameter in order to avoid electrolyte fracture.
  • US2009221421 describes a catalyst for producing hydrogen comprising a porous body, as a support, comprising either one of an amorphous phase oxide and a composite oxide con- taining titanium and zirconium in which titanium has a mol ratio of 5 to 75 percent and zirconium has a mol ratio of 25 to 95 percent to the sum of these two, the porous body having a micro-hole diameter distribution peak in the range of 3 nm to 30 nm; and catalytic active metal grains carried on the a gas contact surface of the support, and the cata ⁇ lytic active metal has a content of 1 to 30 percent by mass to the sum of the porous body and the catalytic active met ⁇ al, and a method of manufacturing thereof. This suppresses sintering or coking causing activity deterioration, thereby minimizing reaction ratio variations with time.
  • a fuel re ⁇ former having the above catalyst, and a fuel cell having the fuel reformer are also described.
  • an electrode layer for fuel cells which is improved in the efficiency of a catalyst, the diffusion ca ⁇ pability of fuel, the stabilization and the high output is disclosed.
  • An electrode for fuel cells which consists of current collector layer which consists of a conductive fi ⁇ ber, and a catalyst layer formed on current collector lay ⁇ er, the conductivity of the thickness direction of the lay ⁇ er in a catalyst layer is raised by using the carbon nano fiber which grew perpendicularly to plane of current collector as a catalyst layer.
  • US2009068523 discloses a fuel electrode for a solid oxide electrochemical cell including: an electrode layer 12 con- stituted of a mixed phase including an oxide having mixed conductivity and another oxide selected from the group in ⁇ cluding an aluminum-based oxide and a magnesium-based com ⁇ posite oxide, said another oxide having, supported on a surface part thereof, particles of at least one member se- lected from nickel, cobalt, and nickel-cobalt alloys; a meshy wiring formed on a surface layer part of the elec ⁇ trode layer and made of a material having higher electronic conductivity than the electrode layer; and a current col ⁇ lector which overlies the electrode layer and is in contact with at least the wiring.
  • the ratio by volume of the first phase to the second phase ranges from 80:20 to 50:50, and particularly from 70:30 to 60:40.
  • the porosity of the entire anode ranges between 15 and 50 per ⁇ cent by volume.
  • the anode additionally comprises a catalyst in the amount of no more than 15 percent of the total vol ⁇ ume, which is disposed on the surface of the pores of the ceramic structure.
  • a temperature profile is pre ⁇ sent across the cell, and the maximum temperature of the profile should always be lower than the reduction tempera ⁇ ture .
  • the invention is to use the knowledge about the Anode Sup ⁇ port creep during reduction to design a reduction process, where the temperature during the beginning of the reduction is kept higher, with a safety margin, than the highest tem- perature during normal operation.
  • the reduction process should not necessarily compensate for any unforeseen operation situation. If operation instructions are not complied with, or if a break-down of a support system component occurs, the temperature of the SOC may rise above the intend- ed operation temperature. However this is not a normal oc ⁇ currence, and the present invention does not necessarily provide a solution for unexpected temperature occurrences, since that would mean a reduction process with high temperatures and an undefined temperature regime, since it is not known what temperatures would occur at unexpected operation situations.
  • the present invention is therefore designed for the intended, expected operation temperatures of an SOC and an SOC stack.
  • the SOC stack is reduced at app. 810 °C and operated at a maximum temperature of app. 800°C.
  • Solid Oxide Cell further comprises one or more barrier layers.
  • anode support comprises a cermet of NiO and YSZ and the activation is done by reducing the NiO into Ni .
  • Solid Oxide Cell produced in a process according to any of the preceding features, wherein the electrolyte of the cell is kept under compression by the anode support at all temperatures at, and below the reduction temperature.
  • Fig. 1 shows a diagram of the effect of different reduction temperatures of an SOC.
  • the diagram of Fig. 1 has on the X-axis the reduction temperature and on the Y-axis the height of the cell curvature for a half cell according to the invention.
  • Fig. 1 shows a plot of the results.
  • the lower curve repre- sents the modelled curvature of the TOFC cells unreduced after sintering as a function of sintering temperature.
  • the three short lines at the far right (1200°C) of the dia ⁇ gram show the measured curvature of the cells used in the experiments sintered at app . 1200°C.
  • the longest, top curve shows the calculated curvature of the reduced cells as a function of reduction temperature, assuming that Anode Support creep happens and the cell is relaxed at the reduction temperature.
  • the three round markers and the middle curve is the experi mental data after varying the reduction temperature, which is in good consistency with the calculated values. This proofs the theory of the invention is working in practice.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Engineering & Computer Science (AREA)
  • General Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Thermal Sciences (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Composite Materials (AREA)
  • Ceramic Engineering (AREA)
  • Inert Electrodes (AREA)
  • Fuel Cell (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Secondary Cells (AREA)

Abstract

Initial reduction temperature of an SOC is kept higher than the highest intended operation temperature of the SOC to keep the electrolyte under compression by the Anode Support at all temperatures equal to and below the maximum intended operation temperature.

Description

Title: Anode Support Creep
FIELD OF THE INVENTION The invention relates to a production process for a solid oxide cell (SOC) , in particular a solid oxide fuel cell (SOFC) stack system or a solid oxide electrolysis cell (SOEC) stack system. Specifically the invention concerns a process to control the anode support creep during reduction to control thermo-mechanical stress in cells in SOC stacks.
BACKGROUND OF THE INVENTION
In the following, the structure of a solid oxide cell stack is explained in relation to fuel cells. The fuel cells may however also run in "reverse mode" and thus operate as electrolysis cells.
A Solid Oxide Fuel Cell (SOFC) comprises a solid electro- lyte that enables the conduction of oxygen ions, a cathode where oxygen is reduced to oxygen ions and an anode where hydrogen is oxidised. The overall reaction in an SOFC is that hydrogen and oxygen electrochemically react to produce electricity, heat and water. In order to produce the re- quired hydrogen, the anode normally possesses catalytic ac¬ tivity for the steam reforming of hydrocarbons, particularly natural gas, whereby hydrogen, carbon dioxide and carbon monoxide are generated. Reforming of methane, the main com¬ ponent of natural gas, can be described by the following reactions:
CH4 + H20 —► CO + 3H2 (steam reforming) CH4 + C02 —► 2CO + 2H2 (dry reforming)
CO + H20 —► C02 + H2 (water-gas-shift)
During operation an oxidant such as air is supplied to the solid oxide fuel cell in the cathode region. Fuel such as hydrogen is supplied in the anode region of the fuel cell. Alternatively, a hydrocarbon fuel such as methane is sup¬ plied in the anode region, where it is converted to hydro¬ gen and carbon oxides by the above reactions. Hydrogen passes through the porous anode and reacts at the anode/- electrolyte interface with oxygen ions generated on the cathode side that have diffused through the electrolyte. Oxygen ions are created in the cathode side with an input of electrons from the external electrical circuit of the cell.
To increase voltage, several cell units are assembled to form a stack and are linked together by interconnects. In¬ terconnects normally serve as a gas barrier to separate the anode (fuel) and cathode (air/oxygen) sides of adjacent cell units, and at the same time they enable current con¬ duction between the adjacent cells, i.e. between an anode of one cell with a surplus of electrons and a cathode of a neighbouring cell needing electrons for the reduction pro- cess. Further, interconnects are normally provided with a plurality of flow paths for the passage of fuel gas on one side of the interconnect and oxidant gas on the opposite side . The way the anode and cathode gas flows are distributed in an SOFC stack is by having a common manifold for each of the two process gasses. The manifolds can either be inter- nal or external. The manifolds supply process gasses to the individual layers in the SOFC stack by the means of chan¬ nels to each layer. The channels are normally situated in one layer of the repeating elements which are comprised in the SOFC stack, i.e. in the spacers or in the interconnect.
The SOC is a combination of several layers all with differ¬ ent Thermal Expansion Coefficients (TEC) . During production of the SOC, the layers are sintered to¬ gether in a way that puts the thin electrolyte in compres¬ sion by the thicker Anode Support. This is achieved by sin¬ tering the layers together at high temperature (app.
1200°C) and by the fact that the TEC of the electrolyte is lower than the Anode Support. This means that the Anode Support will contract more than the electrolyte during cooling from the 1200°C, and thereby put the electrolyte in compression . The reason for putting the thin electrolyte under compres¬ sion by the Anode Support is that the thin layer will frac¬ ture easily if it is under tension, whereas the thick Anode Support can handle the tension better. The electrolyte will be in compression for all temperatures below the sintering temperature, but will be in tension at temperatures above the sintering temperature.
In the sintering stage, the Anode Support comprises a cer¬ met of NiO and YSZ. To activate the Anode and Anode Sup- port, the NiO has to be reduced into Ni . This reduction of the SOC is done after assembly and conditioning of the SOC stack at a temperature above 500 °C - the reduction tempera¬ ture .
It has been discovered that the Anode Support creeps very fast during the beginning of the reduction of NiO to Ni, which means that the internal stress in the SOC is relaxed, the electrolyte is no longer in compression by the Anode Support ! When the first part of the reduction is done, the creep rate of the Anode is "back to normal", which means that in a practical aspect, it does not creep anymore. This means that cooling the stack from the reduction temperature will again put the electrolyte under compression, because of the difference in TEC between the Anode Support and the elec¬ trolyte. But as the case was with the sintering tempera¬ ture, the electrolyte is only in compression for tempera¬ tures below the reduction temperature. When the SOC stack is put into operation, it is vital for the integrity of the electrolyte that it is under compres¬ sion in all places at all times. The operation temperature of the SOC stack compared to the reduction temperature is thus an important parameter in order to avoid electrolyte fracture.
US2009221421 describes a catalyst for producing hydrogen comprising a porous body, as a support, comprising either one of an amorphous phase oxide and a composite oxide con- taining titanium and zirconium in which titanium has a mol ratio of 5 to 75 percent and zirconium has a mol ratio of 25 to 95 percent to the sum of these two, the porous body having a micro-hole diameter distribution peak in the range of 3 nm to 30 nm; and catalytic active metal grains carried on the a gas contact surface of the support, and the cata¬ lytic active metal has a content of 1 to 30 percent by mass to the sum of the porous body and the catalytic active met¬ al, and a method of manufacturing thereof. This suppresses sintering or coking causing activity deterioration, thereby minimizing reaction ratio variations with time. A fuel re¬ former having the above catalyst, and a fuel cell having the fuel reformer are also described.
In US2002177032 an electrode layer for fuel cells which is improved in the efficiency of a catalyst, the diffusion ca¬ pability of fuel, the stabilization and the high output is disclosed. An electrode for fuel cells which consists of current collector layer which consists of a conductive fi¬ ber, and a catalyst layer formed on current collector lay¬ er, the conductivity of the thickness direction of the lay¬ er in a catalyst layer is raised by using the carbon nano fiber which grew perpendicularly to plane of current collector as a catalyst layer.
US2009068523 discloses a fuel electrode for a solid oxide electrochemical cell including: an electrode layer 12 con- stituted of a mixed phase including an oxide having mixed conductivity and another oxide selected from the group in¬ cluding an aluminum-based oxide and a magnesium-based com¬ posite oxide, said another oxide having, supported on a surface part thereof, particles of at least one member se- lected from nickel, cobalt, and nickel-cobalt alloys; a meshy wiring formed on a surface layer part of the elec¬ trode layer and made of a material having higher electronic conductivity than the electrode layer; and a current col¬ lector which overlies the electrode layer and is in contact with at least the wiring. US2010028757 relates to an anode for a high-temperature fuel cell having an anode substrate and/or a functional an¬ ode layer, comprising a porous ceramic structure having a first predominantly electron-conducting phase with the general empirical formula Srl-xLnxTi03 wherein Ln=Y, Gd to Lu and 0.03<x<0.2, and having a second predominantly ion- conducting phase component comprising yttrium or scandium- stabilized zirconium dioxide (YSZ or ScSZ) . In the anode substrate and/or the functional anode layer, the ratio by volume of the first phase to the second phase ranges from 80:20 to 50:50, and particularly from 70:30 to 60:40. The porosity of the entire anode ranges between 15 and 50 per¬ cent by volume. The anode additionally comprises a catalyst in the amount of no more than 15 percent of the total vol¬ ume, which is disposed on the surface of the pores of the ceramic structure.
None of the above described known art provides a solution to the above described problems of keeping the electrolyte under compression at all times of operation of the SOC or SOC stack.
With reference to the above listed considerations, there is a need for a method to ensure that the operation tempera¬ ture of the SOC at all times anywhere in the SOC is lower than the reduction temperature to ensure compression of the electrolyte to avoid fracture. These and other objects are achieved by the invention as described below.
SUMMARY OF THE INVENTION
During operation of the SOC, a temperature profile is pre¬ sent across the cell, and the maximum temperature of the profile should always be lower than the reduction tempera¬ ture .
The invention is to use the knowledge about the Anode Sup¬ port creep during reduction to design a reduction process, where the temperature during the beginning of the reduction is kept higher, with a safety margin, than the highest tem- perature during normal operation. The reduction process should not necessarily compensate for any unforeseen operation situation. If operation instructions are not complied with, or if a break-down of a support system component occurs, the temperature of the SOC may rise above the intend- ed operation temperature. However this is not a normal oc¬ currence, and the present invention does not necessarily provide a solution for unexpected temperature occurrences, since that would mean a reduction process with high temperatures and an undefined temperature regime, since it is not known what temperatures would occur at unexpected operation situations. The present invention is therefore designed for the intended, expected operation temperatures of an SOC and an SOC stack. In an embodiment of the invention, the SOC stack is reduced at app. 810 °C and operated at a maximum temperature of app. 800°C. Features of the invention .
1. Process for activating an anode and an anode support comprised in a Solid Oxide Cell by reduction of the Solid Oxide Cell, the Solid Oxide Cell further comprising an electrolyte and a cathode, the process comprising the step of -
• heating the Solid Oxide Cell to a reduction tempera¬ ture higher than the maximum intended operation tem- perature of the Solid Oxide Cell, whereby the electro¬ lyte is kept under compression by the anode support during operation.
2. Process according to feature 1, wherein the Solid Oxide Cell further comprises one or more barrier layers.
3. Process according to feature 1 or 2, wherein the solid Oxide cell further comprises one or more contacting layers. 4. Process according to feature 1, wherein the reduction temperature of the Solid Oxide Cell is above 800°C.
5. Process according to feature 1, wherein the reduction temperature of the Solid Oxide Cell is above 775°C.
6. Process according to feature 1, wherein the reduction temperature of the Solid Oxide Cell is above 750°C.
7. Process according to feature 1, wherein the reduction temperature of the Solid Oxide Cell is above 700°C. 8. Process according to feature 1, wherein the reduction temperature of the Solid Oxide Cell is above 600°C.
9. Process according to feature 1, wherein the reduction temperature of the Solid Oxide Cell is above 500°C.
10. Process according to feature 1, wherein the reduction temperature of the Solid Oxide Cell is the maximum intended operation temperature plus a temperature range, Δ .
11. Process according to feature 10, wherein ΔΤ is 0 - 500°C, preferably 0 - 300°C, preferably 0 - 100°C.
12. Process according to any of the preceding features, wherein the anode support comprises a cermet of NiO and YSZ and the activation is done by reducing the NiO into Ni .
13. Process according to any of the preceding features, wherein the CTE of the electrolyte is lower than the CTE of the anode support.
14. Solid Oxide Cell produced in a process according to any of the preceding features, wherein the electrolyte of the cell is kept under compression by the anode support at all temperatures at, and below the reduction temperature. BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further illustrated by the accompanying drawing showing an example of an embodiment of the inven- tion.
Fig. 1 shows a diagram of the effect of different reduction temperatures of an SOC. DETAILED DESCRIPTION
The diagram of Fig. 1 has on the X-axis the reduction temperature and on the Y-axis the height of the cell curvature for a half cell according to the invention.
To investigate the Anode Support creep as described above, the effect of different reduction temperatures were mod¬ elled and tested on three SOC stacks. Curvature of the cells was used as a measure of the inter¬ nal stress in the cells at room temperature caused by the difference in TEC.
Fig. 1 shows a plot of the results. The lower curve repre- sents the modelled curvature of the TOFC cells unreduced after sintering as a function of sintering temperature.
The three short lines at the far right (1200°C) of the dia¬ gram show the measured curvature of the cells used in the experiments sintered at app . 1200°C. The longest, top curve shows the calculated curvature of the reduced cells as a function of reduction temperature, assuming that Anode Support creep happens and the cell is relaxed at the reduction temperature.
The three round markers and the middle curve is the experi mental data after varying the reduction temperature, which is in good consistency with the calculated values. This proofs the theory of the invention is working in practice.

Claims

CLAIMS .
1. Process for activating an anode and an anode support comprised in a Solid Oxide Cell by reduction of the Solid Oxide Cell, the Solid Oxide Cell further comprising an electrolyte and a cathode, the process comprising the step of -
• heating the Solid Oxide Cell to a reduction tempera¬ ture higher than the maximum intended operation tem- perature of the Solid Oxide Cell, whereby the electro¬ lyte is kept under compression by the anode support during operation.
2. Process according to claim 1, wherein the Solid Oxide Cell further comprises one or more barrier layers.
3. Process according to claim 1 or 2, wherein the solid Oxide cell further comprises one or more contacting layers.
4. Process according to claim 1, wherein the reduction temperature of the Solid Oxide Cell is above 800°C.
5. Process according to claim 1, wherein the reduction temperature of the Solid Oxide Cell is above 775°C.
6. Process according to claim 1, wherein the reduction temperature of the Solid Oxide Cell is above 750°C.
7. Process according to claim 1, wherein the reduction tem- perature of the Solid Oxide Cell is above 700°C.
8. Process according to claim 1, wherein the reduction temperature of the Solid Oxide Cell is above 600°C.
9. Process according to claim 1, wherein the reduction tem- perature of the Solid Oxide Cell is above 500°C.
10. Process according to claim 1, wherein the reduction temperature of the Solid Oxide Cell is the maximum intended operation temperature plus a temperature range, Δ .
11. Process according to claim 10, wherein ΔΤ is 0 - 500°C, preferably 0 - 300°C, preferably 0 - 100°C.
12. Process according to any of the preceding claims, wherein the anode support comprises a cermet of NiO and YSZ and the activation is done by reducing the NiO into Ni .
13. Process according to any of the preceding claims, wherein the CTE of the electrolyte is lower than the CTE of the anode support.
14. Solid Oxide Cell produced in a process according to any of the preceding claims, wherein the electrolyte of the cell is kept under compression by the anode support at all temperatures at, and below the reduction temperature.
PCT/EP2015/064392 2014-06-27 2015-06-25 Anode support creep Ceased WO2015197767A1 (en)

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AU2015279216A AU2015279216B2 (en) 2014-06-27 2015-06-25 Anode support creep
CA2952338A CA2952338C (en) 2014-06-27 2015-06-25 Process to control anode support creep for controlling thermo-mechanical stress in solid oxide cell stacks
JP2016574222A JP6894705B2 (en) 2014-06-27 2015-06-25 Anode support creep
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