Preparation And Properties Of Ni-and Co-based Cathode Materials For Intermediate-temperature Solid Oxide Fuel Cells

A conventional solid oxide fuel cell (SOFC) consists of the anode, cathode andelectrolyte. Cathode material must have the ability to reduce oxygen, transport oxygenions and electrons. Lanthanum Strontium Manganite (LSM) cathode material is usedas cathode in traditional SOFCs. The traditional SOFCs have to be operated attemperatures above800C in order to obtain a desirable power density, and the highoperating temperature makes traditional SOFCs unable to satisfy the commercialexpectations. This is mainly due to the long-term degradation problems associatedwith the high operating temperature. Therefore, intermediate-temperature solid oxidefuel cells (IT-SOFCs) have received great attention. IT-SOFCs are operating between600and800C, therefore LSM does not possess sufficient catalytic efficiency. Sodevelopment of a cathode material with good performance inintermediate-temperature range is very important for IT-SOFCs to be used in practicalapplication. Generally, cobalt-based peroveskite materials display higher ionic andelectronic conductivities than other cathode materials in intermediate-temperaturerange. Therefore, the use of cobalt-based cathode materials can result in a low cathodepolarization resistance. However, such cobalt-based cathodes result in an increasedthermal expansion coefficient, which may result in a delamination at thecathode/electrolyte interface or cracking of the electrolyte. Iron-doped nickelateexhibits an attractive combination of electronic transport properties, a moderatethermal expansion and phase stability at intermediate temperature in air.，making itbecome a promising cathode material for IT-SOFC.A cobalt-free orthorhombic perovskite oxide, PrNi0.6Fe0.4O3δ(PNF), issynthesized by the EDTA-citrate complexing method and assessed as a potentialcathode material for IT-SOFCs. XRD result shows the PNF material has a good chemical compatibility with Ce0.8Sm0.2O1.9(SDC) electrolyte below950C. PNFcathode exhibits a highest electrical conductivity of98S cm1at850C in air. Theaverage thermal expansion coefficient (TEC) of the PNF specimen is11.2×106K1between30and950C in air. The area specific resistance (ASR) value of the PNFcathode on SDC electrolyte is0.202Ω cm2at800C and it is decreased to0.013Ωcm2after the PNF cathode is impregnated with SDC. The maximum power density ofsingle cell with the PNF cathode on a300μm–thick SDC electrolyte is331mW cm2at800C and it reaches544mW cm2after the PNF cathode is impregnated withSDC. The SDC-impregnated PNF cathodes also exhibit a good electrochemicalstability for the single-cell performance decreases gently after a20h-test. Theseresults imply that the PNF has a potential use as a cathode material for IT-SOFCs, andion impregnation is an effective way to improve the cathode performance.SrCo0.95Mo0.05O3δand SrCo0.9Mo0.1O3δare synthesized by the EDTA-citratecomplexing method and assessed as a potential cathode material for IT-SOFCs. XRDresults show both of the material have a tetragonal structure and no impurity phaseappearance when the samples fired at1000C for10h. Both of the material have agood chemical compatibility with SDC and LSGM at950C for10h.SrCo0.95Mo0.05O3δmaterial exhibits a highest electrical conductivity of286S cm-1at400C and SrCo0.95Mo0.05O3δmaterial exhibits a highest electrical conductivity of170S cm-1at350C. Both of the materials exhibit high average TECs. The ASRvalue of the SrCo0.95Mo0.05O3δcathode on LSGM electrolyte is0.020Ω cm2at800C and SrCo0.9Mo0.1O3δcathode has an ASR value of0.026Ω cm2at the sametemperature. The maximum power density of single cell with the SrCo0.95Mo0.05O3δcathode on a300μm-thick LSGM electrolyte is795mW cm2at800C and themaximum power density of single cell with the SrCo0.9Mo0.1O3δcathode is687mWcm2under the same condition. All of results indicate that both of the materials havepotential use as IT-SOFC cathode materials.