Atomically dispersed Mn-N_x catalysts derived from Mn-hexamine coordination frameworks for oxygen reduction reaction

Metal-organic frameworks recently have been burgeoning and used as precursors to obtain various metal-nitrogen-carbon catalysts for oxygen reduction reaction (ORR). Although rarely studied, Mn-N-C is a promising catalyst for ORR due to its weak Fenton reaction activity and strong graphitization catalysis. Here, we developed a facile strategy for anchoring the atomically dispersed nitrogen-coordinated single Mn sites on carbon nanosheets (MnNCS) from an Mn-hexamine coordination framework. The atomically dispersed Mn-N-4 sites were dispersed on ultrathin carbon nanosheets with a hierarchically porous structure. The optimized MnNCS displayed an excellent ORR performance in half-cells (0.89 V vs. reversible hydrogen electrode (RHE) in base and 0.76 V vs. RHE in acid in half-wave potential) and Zn-air batteries (233 mW cm(-2) in peak power density), along with significantly enhanced stability. Density functional theory calculations further corroborated that the Mn-N-4-C-12 site has favorable adsorption of *OH as the rate-determining step. These findings demonstrate that the metal-hexamine coordination framework can be used as a model system for the rational design of highly active atomic metal catalysts for energy applications.