Unfolding BOB Bonds for an Enhanced ORR Performance in ABO3-Type Perovskites

Abstract

Identifying the relationship between catalytic performance and material structure is crucial to establish the design principle for highly active catalysts. Deficiency in BO bond covalency induced by lattice distortion severely restricts the oxygen reduction reaction (ORR) performance for ABO3-type perovskite oxides. Herein, a rearrangement of hybridization mode for BO bond is used to tune the overlap of the electron cloud between B 3d and O 2p through A-stie doping with larger radius ions. The BO bond covalency is strengthened with a BOB bond angle recovered from intrinsic structural distortion. As a result, the adsorption and the reduction process for O2 on the oxide surface can be promoted via shifting the O-2p band center toward the Fermi Level. Simultaneously, the spin electrons in the Mn 3d orbit become more parallel. It will lead to a high electrical conductivity by the enhanced double exchange process and thereof mitigate the ORR efficiency loss. Further density functional theory calculation reveals that a flat [BO2] plane will make contribution to the charge transfer process from lattice oxygen to adsorbed oxygen (mediated with B ions). Through such exploration of the effect of crystal structure on the electronic state of perovskite oxides, a novel insight into design of highly active ORR catalysts is offered.