Design principles for oxygen-reduction activity on perovskite oxide catalysts for fuel cells and metal-air batteries

The prohibitive cost and scarcity of the noble-metal catalysts needed for catalysing the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries limit the commercialization of these clean-energy technologies. Identifying design principle that links material properties to the catalytic activity can accelerate the search for highly active and abundant transition-metal-oxide catalysts to replace platinum. Here, we demonstrate that the ORR activity for oxide catalysts primarily correlates to sigma*-orbital (e(g)) occupation and the extent of B-site transition-m covalency, which serves as a secondary activity descriptor. Our findings reflect the critical influences of the sigma* orbital and metal-oxygen covalency on the competition between O-2(2-)/OH- displacement and OH- regeneration surface transition-metal ions as the rate-limiting steps of the ORR, and thus highlight the importance of electronic structure in controlling oxide catalytic activity.