Coating internal surface of porous electrode for decreasing the ohmic resistance and shifting oxygen reduction reaction pathways in solid oxide fuel cells

Abstract

For mixed conductor La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) in solid oxide fuel cells (SOFCs), cation surface segregation such as volatile Sr and consequently losing conductivity and active sites for the oxygen reduction reaction (ORR) are problematic. To mitigate the cation segregation, a practical approach is to apply a conformal surface coating. Nevertheless, the coating layer would inevitably alter the ORR pathways that initially take place on the backbone surface. In this study, the unary electrocatalyst of Pt or CoOx was applied to the LSCF/Sm-doped CeO2 (SDC) composite electrode of inherently functional SOFCs. Both ALD coating layers evolve strong interaction with the composite cathode. Upon operations, the Pt coating layer remains conformal on LSCF grain surfaces but turns into discrete particles on SDC. For the CoOx coating, the conformal layer grows to be the discrete nano-grains on both the LSCF and SDC grains. ALD coating of the cathode alone reduces the cell ohmic resistance. The ALD-induced conductivity change is ascribed to different mechanisms. This study presents a novel and feasible approach to apply a conformal, dense coating layer on the surface of a mixed conductor, simultaneously increasing the conductivity and durability of the SOFC cathode.