Molecular Insights into Active Sites of Manganese Oxide Based Water Oxidation Eletrocatalysts

Manganese oxides (MnO_x) are promising candidates for water oxidation catalysts. However, the true active centers remain elusive due to the dynamic nature of MnO_x during electrolysis and/or activation, hindering progress in catalyst design and optimization. Herein, we aim to address such a challenge by preparing a defective cubical tri-manganese complex and a di-manganese complex to mimic the in-plane and on-edge subunits of birnessite-like heterogeneous MnO_x electrocatalysts. Electrochemical results indicate that the defective cubical tri-manganese complex is a robust molecular catalyst to facilitate 4e^- water oxidation to produce O₂ with an optimal Faradic efficiency of 95% and an average rate of oxygen generation of 46.4 µmol h cm^-2, which is among the highest values of reported manganese-based molecular catalysts and is comparable with representative heterogeneous MnO_x systems. In contrast, the di-manganese complex exhibits marginal catalytic activity. This work provides molecular insights into the true active centers of MnO_x and aids in the precise design of more efficient MnO_x water oxidation electrocatalysts.