Electrochemically influenced cation inter-diffusion and Co3O4 formation on La0.6Sr0.4CoO3 infiltrated into SOFC cathodes

Abstract

Nanosized LSC electrocatalyst was infiltrated into a porous scaffold cathode composed of Sm2O3-doped CeO2 (SDC) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) in a commercial button solid oxide fuel cell (SOFC). To understand the stability of cathodes infiltrated with LSC, the infiltrated composite cells were subjected to both electrochemical operating and thermal aging states at 750°C for 1500h. Nanostructure and local chemistry evolution of La0.6Sr0.4CoO3 (LSC) infiltrated cathodes upon operation and aging were investigated by transmission electron microscopy. After operation, the LSC remained a cubic perovskite, and the crystal grains exhibit comparable size to as-infiltrated LSC grains. Inter-diffusion of Fe from the LSCF to a Fe-incorporated LSC layer developed on the LSCF backbone. However, only sharp interfaces were observed between LSC and SDC backbone in the as-infiltrated cathode and such interfaces remain after operation. The infiltrated LSC on the SDC backbone also retains granular particle morphology. Furthermore, newly grown Co3O4 nanocrystals were found in the operated cathode. After thermal aging, on the other hand, cation inter-diffusion across the interfaces of the infiltrate particles and the cathode backbones is less than that from the operated cells. The following hypothesis is proposed: Co3O4 forms on LSC arising from local charge balancing between cobalt and oxygen vacancies.