Optimization Of Perovskite-type LSCN Cathode Material And Microstructure For It-SOFCs

Solid oxide fuel cell （SOFC） is purported to be a promising power device to solve powerproblems in modern society based on its features of energy-economy, high-efficiency andeco-friendly. To promote commercialization of SOFC needs to reduce the operationtemperature to mediate scale （600～800°C） in order to drop down the system cost, enlargealternative material categories and improve system stability. However, as temperaturegoes down, the falling catalytic activity in cathodes becomes a major reason of limitedpower density. In this article, perovskite-type La_1-xSr_xCo_1-yNi_yO₃（LSCN） is studied as analternative IT-SOFCs cathode material and its electrochemical properties is optimized byinfiltration method.Perovskite-type LSCN powder with different stoichiometric ratios are synthesized bypolymer-assisted combustion method and their basic properties are compared. The resultsindicate that La_0.8Sr_0.2Co_0.8Ni_0.2O₃possesses the best properties with the total conductivityof1201s/cm and TEC of15.3×10-6K-1at800, which are better than traditonal LSCFand LSM perovskite materials.Infiltrated La_0.8Sr_0.2Co_0.8Ni_0.2O₃+Gd-doped CeO₂（LSCN+GDC） cathodes are preparedand their electrochemical performances are evaluated and compared with the conventionalscreen printed LSCN cathodes. The results indicate that the cathode performance can beenhanced by the presence of the nanosized microstructure produced with the solutionimpregnation method. It is determined that the amount of LSCN loading in the LSCN+GDC composite cathode needs to be higher than35wt%in order to achieve aperformance superior to that of the conventional LSCN cathode. The optimum amount ofLSCN loading is in the range of45～55wt%with an activation energy near127.3KJ/molfor oxygen reduction. At temperatures between600and750°C, the polarization resistanceof the55wt%LSCN loaded LSCN+GDC cathode is in the range of1.07and0.08cm²,which is only about one half of that for the conventional cathode.Current treatment is used to both cathodes fabricated by screen printing and infiltration toanalyze long term stability of LSCN cathode.55wt%LSCN+GDC cathode shows declineof electrochemical performance even at the beginning of the current treatment and its heattreatment results indicate that nano-sized LSCN grains have strong growing tendency.The sintering between nano-grain LSCN is spotted clearly for55wt%LSCN+GDC and thecathode polarization resistance is increased to0.17cm²at750°C after100hours currenttreatment. To further understand the performance change with testing time, theelectrochemical impedance spectras are fitted with an equivalent circuit. The resultssuggest that the mass transfer process is the main reason of the overall decrease inLSCN+GDC cathode. Hence, how to maintain stability of infiltrated nano-sturcture stillneeds further studying.