The Preparation And Performance Study Of Y-modified NiFe₂O₄ Spinel Coatings For SOFC Metallic Interconnect Applications

With the decrease of operating temperature of solid oxide fuel cells?SOFCs?,it's possible to use metal alloys as interconnect.Compared with the ceramic interconnect,the metal interconnect has the advantages of such as low-cost and facile processing.Specially,the Fe-Cr alloy has been paid more attention to as the SOFC interconnect,because it matches the expansion coefficient of other components of SOFC.However,Fe-Cr alloys are prone to high-temperature oxidation in the SOFC working environment,which will cause Cr volatilization,"Cr poisoning"and other negative consequences,resluting in the decrease of performance in battery.At present,the method of applying protective coating on the surface of metal interconnect is mainly used to improve the problems mentioned above.The spinel coating has become a hot spot for researchers due to its excellent performance.But in the working environment after a long period of high temperature oxidation,the thickness of the transition layer between the coating and the substrate will increase of Cr,which not only increases the surface Area Specific Resistance?ASR?of the coating/alloy interface,reduces the conductivity,but also leads to the decrease of the adhesion between the coating and the substrate,which causes the coating to peel off and make the battery failure.The addition of a small amount of rare earth elements in spinel coating can increase the bonding strength between the coating and the substrate,and significantly improve the oxidation resistance and electrical conductivity of the substrate.But so far,there are few reports on rare earth elements in improving the performance of Ni-Fe spinel coating of solid oxide fuel cell.In this paper,rare earth Y modified NiFe₂O₄ powder with good crystallinity was obtained by sol-gel process.On this basis,the rare earth Y modified NiFe₂O₄ spinel protective coating was successfully prepared on the surface of Fe-Cr alloy by low cost electrophoretic deposition process.The effects of rare earth doping on the phase,microstructure,morphology and high-temperature properties of the coating were discussed.The main conclusions are as follows:?1?With nickel nitrate,ferric nitrate and cerium nitrate as starting materials,citric acid as ligand,pH=5,stirring process parameters as 75°C,600 r/min and 2 h,drying at 80°C for 24 h,doping amount of rare earth is as 0.5 mol·L^-1,sintering at 800°C for 3 h in air,the Y doped NiFe₂O₄ spinel powder with stable phase and good crystallinity is prepared;?2?With acetone as the liquid base,the spinel powder loading capacity as 40 g·L^-1 and the concentration of nuclear power regulator as about 0.8 mmol·L^-1,the stable suspension can be obtained.With deposition voltage as 150 V,deposition time as 150 s,drying at 80°C for 24h,sintering at 800°C for 3 h in reductive atmosphere first and then sintering at 1100°C for 3 h in air,the spinel coating with uniform and dense structure was obtained;?3?The rare earth elements can effectively refine the grain,improve the microstructure and increase the adhesion between coating and substrate.The oxidation rate constant of Y modified NiFe₂O₄ coating is 7.55×10^-4mg²·cm^-4·h^-1 after cyclic oxidation at 800°C for 168 h in air.The ASR value of the modified coating was basically stable at 15.4 m?·cm²,which was significantly lower than that of uncoated substract.