Defective and c-Disordered Hortensia-like Layered MnOx as an Efficient Electrocatalyst for Water Oxidation at Neutral pH

The development of a highly active manganese-based water oxidation catalyst in the design of an ideal artificial photosynthetic device operating under neutral pH conditions remains a great challenge, due to the instability of pivotal Mn3+ intermediates. We report here defective and c-disordered layered manganese oxides (MnOx-300) formed on a fluorine-doped tin oxide electrode by constant anodic potential deposition and subsequent annealing, with a catalytic onset (0.25 mA/cm(2)) at an overpotential (eta) of 280 mV and a benchmark catalytic current density of 1.0 mA/cm(2) at an overpotential (eta) of 330 mV under neutral pH (1 M potassium phosphate). Steady current density above 8.2 mA/cm(2) was obtained during the electrolysis at 1.4 V versus the normal hydrogen electrode for 20 h. Insightful studies showed that the main contributing factors for the observed high activity of MnOx-300 are (i) a defective and randomly stacked layered structure, (ii) an increased degree of Jahn-Teller distorted Mn3+ in the MnO6 octahedral sheets, (iii) effective stabilization of Mn3+, (iv) a high surface area, and (v) improved electrical conductivity. These results demonstrate that manganese oxides as structural and functional models of an oxygen-evolving complex (OEC) in photosystem II are promising catalysts for water oxidation in addition to Ni/Co-based oxides/hydroxides.