CaMn7O12 Quadruple Perovskite Oxides Proceed by Two‐Active‐Site Reaction Mechanism for the Oxygen Evolution Reaction

Abstract The oxygen evolution reaction (OER) is one of the essential energy conversion reactions for hydrogen production. In quadruple perovskite oxides AA’ 3 B 4 O 12 (A=Ca, Sr, A’=Cu, Mn and B=3d metals), the new reaction mechanism of O−O bond formation between adsorbed oxygen species at adjacent A’‐B sites has been proposed in recent studies. This idea of multiple transition metals working together to form an active site, rather than a single active site, is appealing, but has not been systematically investigated so far. This study examined catalytic OER performances of CaMn 7 O 12 quadruple perovskite oxides with precisely controlled Mn(A′)−Mn(B) distance by doping with Sr, Cu and Al. The crystal structure and the state of cations and O were investigated through XRD with Rietveld refinement and X‐ray absorption spectroscopy. The OER catalytic activity is clearly correlated with the distance of Mn(A’)−Mn(B) while both e g state of Mn and O 2p band center unchanged. The shrinkage of the A’‐B distance affects the stability of O−O bond on A’‐B site and accelerates OER kinetics.