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

Abstract

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-L_x). 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-L_x rendering a mass activity of 6680 A g_Fe/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.