Improvement of the Electrochemical Performance of Ln0.58Sr0.4Fe0.8Co0.2O3-δ IT-SOFC Cathodes by Ternary Lanthanide Combinations (La-Pr-Sm)
Résumé
Active perovskite-based SOFC cathodes have been developed through lanthanide combination in the (La1-x-yPrxSmy)0.58Sr0.4Fe0.8Co0.2O3- system following a ternary mixture experimental design. These compositions were prepared through a sol-gel method and characterized by electrochemical impedance spectroscopy (EIS) as symmetrical cells on GDC-electrolyte samples in the 450-650 ºC temperature range. The electrochemical properties of the single lanthanide-based Ln0.58Sr0.4Fe0.8Co0.2O3- compounds were enhanced when different lanthanides were combined together in the same crystalline structure. The observed improvement does not follow a mere additional effect of the performance from the parent Ln0.58Sr0.4Fe0.8Co0.2O3- compounds, i.e. it does not follow a linear behaviour, and the better performance is ascribed to synergetic catalytic effects among lanthanide cations. A reduction in electrode polarization resistance with respect to non-substituted compositions is stated for most Ln0.58Sr0.4Fe0.8Co0.2O3- electrode compositions combining two or three lanthanides. Samarium addition to the electrode material involves a substantial reduction in the activation energy and the reduction degree is directly dependant on the samarium amount incorporated in the lattice. The best performing composition comprises a praseodymium-rich lanthanum-based electrode material. Selected cathode compositions were tested in fully-assembled anode-supported cells and electrochemical characterisation supports the cooperative effect of lanthanide combination.
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