Optimizing Oxygen Reduction Catalyst Morphologies from First Principles

Abstract

Catalytic activity of perovskites for oxygen reduction (ORR) was recently correlated with bulk d-electron occupancy of the transition metal. We expand on the resultant model, which successfully reproduces the high activity of LaMnO[subscript 3] relative to other perovskites, by addressing catalyst surface morphology as an important aspect of the optimal ORR catalyst. The nature of reaction sites on low index surfaces of orthorhombic (Pnma) LaMnO[subscript 3] is established from First Principles. The adsorption of O[subscript 2] is markedly influenced by local geometry and strong electron correlation. Only one of the six reactions sites that result from experimentally confirmed symmetry-breaking Jahn–Teller distortions is found to bind O[subscript 2] with an intermediate binding energy while facilitating the formation of superoxide, an important ORR intermediate in alkaline media. As demonstrated here for LaMnO[subscript 3], rational design of the catalyst morphology to promote specific active sites is a highly effective optimization strategy for advanced functional ORR catalysts.