Inhibition of Charge Disproportionation of MnO2 Electrocatalysts for Efficient Water Oxidation under Neutral Conditions

The development of Mn-oxide electrocatalysts for the oxidation of H2O to O2 has been the subject of intensive researches not only for their importance as components of artificial photosynthetic systems, but also as O2-evolving centers in photosystem II. However, limited knowledge of the mechanisms underlying this oxidation reaction hampers the ability to rationally design effective catalysts. Herein, using in situ spectroelectrochemical techniques, we demonstrate that the stabilization of surface-associated intermediate Mn3+ species relative to charge disproportionation is an effective strategy to lower the overpotential for water oxidation by MnO2. The formation of N–Mn bonds via the coordination of amine groups of poly(allylamine hydrochloride) to the surface Mn sites of MnO2 electrodes effectively stabilized the Mn3+ species, resulting in an ∼500-mV negative shift of the onset potential for the O2 evolution reaction at neutral pH.