Water oxidation on a mononuclear manganese heterogeneous catalyst

Water oxidation is the prerequisite for dioxygen evolution in natural or artificial photosynthesis. Although it has been demonstrated that multinuclear active sites are commonly necessary for water oxidation, as inspired by the natural oxygen-evolving centre CaMn₄O₅, a multinuclear manganese cluster, whether mononuclear manganese can also efficiently catalyse water oxidation has been a long-standing question. Herein, we found that a heterogeneous catalyst with mononuclear manganese embedded in nitrogen-doped graphene (Mn-NG) shows a turnover frequency as high as 214 s⁻¹ for chemical water oxidation and an electrochemical overpotential as low as 337 mV at a current density of 10 mA cm⁻². Structural characterization and density functional theory calculations reveal that the high activity of Mn-NG can be attributed to the mononuclear manganese ion coordinated with four nitrogen atoms embedded in the graphene matrix.