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., CaCu3Fe4O12 and LaMn7O12) displayed catalytic activity that was higher than that of simple perovskites (e.g., LaMnO3), but the reason has not yet been unveiled. We have conducted first-principles calculations of the several surface energies of LaMn7O12 and adsorption energies of OER intermediates on LaMn7O12 using slab models to clarify the reaction mechanism. The Mn-rich surfaces, i.e., the (001) with BO2 termination and (220) surfaces, are found to be more stable for LaMn7O12. It is found that all intermediates are preferentially adsorbed on the A′–B-bridge site on the LaMn7O12 (220) surface, although only the B-top site was a stable adsorption site on the (001) surface of LaMn7O12 and LaMnO3. The difference between theoretical overpotentials on the (220) surface of LaMn7O12 and the (001) surface with BO2 termination of LaMnO3 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.