Degradation of Oxygen Reduction Reaction Kinetics at La0.6Sr0.4Co0.2Fe0.8O3-d Cathodes Aged at Different Temperatures

LAURA BAQUÉ; ADRIANA SERQUIS

Encuentro; 20th Topical Meeting of the International Society of Electrochemistry; 2017

Solid Oxide Fuel Cells (SOFCs) are highly efficient electrochemical devices which convert a wide range of fuels (i.e. hydrogen, methane, carbon monoxide) into electrical energy and heat. This characteristic makes them an extremely attractive solution for the transition period between fossil fuels and hydrogen. Nevertheless, the commercialization of SOFCs is still hindered by their cost and long term degradation. SOFC efficiency and durability is mainly determined by the area specific resistance (ASR) and degradation of the cathode, the electrolyte and the anode. Since the cathode is typically the component with the highest ASR, it is very importantto limit its degradation. This work aims at studying the degradation of the oxygen reduction reaction (ORR) kinetics at La0.6Sr0.4Co0.2Fe0.8O3-d(LSCFO) cathodes induced by aging at different temperatures (i.e. 600, 700 and 800 ºC) in air for 50 h. LSCFO oxide powders were prepared by solid state reaction and deposited on Ce1-xGdxO2-d electrolytes by spin coating. The studied cathodes have an intermediate microstructure between that of a dense pellet and that of a porous film since they are indeed porous but are mainly composed of particles within the micrometric range (as the dense pellets). This particular microstructure was chosen because our preliminary results [1,2] suggest that it facilitates, under the aging conditions mentioned above, the occurrence of one of the most reported degradation mechanisms of LSCFO cathodes: surface  Sr-enrichment. The evolution of the cathode electrochemical properties was continuously monitored by Electrochemical Impedance Spectroscopy (EIS) during the aging treatment while the microstructural changes were characterized by Scanning Electron Microscopy (SEM) before and after the aging treatment. Our EIS analysis, based on the Adler-Lane-Steele model [3], allowed us analyzing separately the evolution of the oxygen ion diffusion and the oxygen surface exchange contributions during the aging treatment without requiring the knowledge of thermodynamic, surface kinetics, transport and microstructural parameters as usual for the ALS model. In addition, the origin of the ORR kinetics degradation and its dependence on the aging temperature were identified.