Ligand‐Tuning Metallic Sites in Molecular Complexes for Efficient Water Oxidation

Metal‐organic hybrid catalysts with highly tunable single‐sites are promising for oxygen‐evolution reaction (OER), but molecular‐scale understanding of underlying reaction mechanisms still remain elusive on these bulk materials. Herein, we report a direct construction of heterogenized molecular complexes stabilized on carbon substrates via coordinating Fe‐Ni sites with four aromatic carboxylate ligands (FeNi‐Lx). The ligands‐tuning π‐π stacking interaction between aromatic carboxylate ligands and carbon supports promote the oxidative charge accumulation on Fe‐Ni sites via fast electron transferring, thus the optimized FeNi‐Lx rendering a mass activity of 6680 A gFe/Ni‐1 at 0.3 V overpotential. In situ characteristics and theoretical analysis demonstrate that the OH‐ nucleophilic attack on hypervalent iron sites induce the reconstruction of active Fe‐O‐Ni species, accompanying with fast valence increasing. Whereas, during OER, the unexpected valence reduction of Fe‐O‐Ni sites would be attributed to the oxygen‐generating from OOH* intermediates. These findings would establish an essential understanding of the origin of active centers in molecular complexes catalysts for oxygen‐evolution.