Activating the Bifunctionality of a Perovskite Oxide toward Oxygen Reduction and Oxygen Evolution Reactions.

This article presents a facile and effective approach to activate the bifunctionality of calcium-manganese perovskites toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). We substituted Nb into the Mn site of CaMnO3 (CMO) and treated the material with H2. The as-obtained CaMn0.75Nb0.25O3-δ (H2-CMNO) displays the same structure as that of CMO, and compared to that of CMO, H2-CMNO exhibits significantly improved OER performance, including a lower overpotential, a reduced Tafel slope, a higher mass activity, and enhanced stability. In addition, the ORR performance of H2-CMNO is also greatly enhanced, relative to CMO, with a higher ORR activity and a more efficient electron-transfer pathway. H2-CMNO shows an even higher activity-per-catalyst cost and superior stability than that of state-of-the-art materials, such as IrO2 and Pt/C. This great enhancement in ORR and OER activity of H2-CMNO is attributed to several factors, including phase stabilization, optimized eg filling, better OH- adsorption, and improved electrical conductivity.