Bifunctional LaMn0.3Co0.7O3 Perovskite Oxide Catalyst for Oxygen Reduction and Evolution Reactions: The Optimized eg Electronic Structures by Manganese Dopant

Perovskite oxides as bifunctional electrocatalysts toward oxygen reduction (ORR) and oxygen evolution reactions (OER) have been investigated for decades because of the flexible and adjustable electronic structures. For example, by optimizing the strength of the Co-O bond, the ORR and OER activity of a typical perovskite oxide, LaCoO₃, can be improved, but they are still unsatisfying. The insufficient insights into the effects of secondary metal dopants at the B-site on the electronic structure and activity, especially for ORR, significantly limit the R&D of bifunctional perovskite oxide catalysts. In this work, a series of LaMn_xCo_1-xO₃ (x = 0, 0.25, 0.3, 0.35, 0.5, 1) catalysts are prepared by a polyol-assisted solvothermal method to investigate the structure-property relationships between the B-site metal substitution and the electrochemical performance of perovskite oxides catalysts. The optimized LaMn_0.3Co_0.7O₃ catalyst demonstrates an enhanced half-wave potential of 0.72 V for ORR, 52 mV higher than that of the pristine LaCoO₃ (0.668 V). Meanwhile, the OER overpotential of LaMn_0.3Co_0.7O₃ catalyst is 416 mV, which is reduced by 64 mV compared to LaCoO₃ (480 mV). It is revealed that the appropriate Mn dopant efficiently optimizes the covalency of Co-O bonds and significantly reduces the e_g orbit-filling electron from 1.23 of pristine LaCoO₃ to 1.02 in LaMn_0.3Co_0.7O₃ (very close to theoretical value 1). This work paves a new way to design and synthesize bifunctional perovskite oxide electrocatalyst for ORR and OER.