Oxygen Evolution via the Bridging Inequivalent Dual-Site Reaction: First-Principles Study of a Quadruple-Perovskite Oxide Catalyst

Abstract

Perovskite-type oxides composed of earth-abundant elements have been extensively studied as possible candidates for oxygen evolution reaction (OER) catalysts. In our recent study, quadruple perovskite oxides (e.g., CaCu 3 Fe 4 O 12 and LaMn 7 O 12 ) displayed catalytic activity that was higher than that of simple perovskites (e.g., LaMnO 3 ), but the reason has not yet been unveiled. We have conducted first-principles calculations of the several surface energies of LaMn 7 O 12 and adsorption energies of OER intermediates on LaMn 7 O 12 using slab models to clarify the reaction mechanism. The Mn-rich surfaces, i.e., the (001) with BO 2 termination and (220) surfaces, are found to be more stable for LaMn 7 O 12 . It is found that all intermediates are preferentially adsorbed on the A′–B-bridge site on the LaMn 7 O 12 (220) surface, although only the B-top site was a stable adsorption site on the (001) surface of LaMn 7 O 12 and LaMnO 3 . The difference between theoretical overpotentials on the (220) surface of LaMn 7 O 12 and the (001) surface with BO 2 termination of LaMnO 3 is in good agreement with the experimental overpotential for OER. We propose a new design principle in which OER is enhanced via adsorption on the A′–B-bridge site consisting of two adjacent Mn sites {coordination-unsaturated pyramid [coordination number (CN) = 5] and coordination-saturated pseudosquare (CN = 4)}, where the adsorbates are strongly bound to the former and weakly bound to the latter.