Non-nitrogen Mn-O4 coordination environment boosting CO2 electroreduction over single-atom Mn catalyst at low overpotential

Modulating the ordinary nitrogen coordination environment of single-atom catalysts (SACs) is a promising strategy for customizing their activity and selectivity in electrochemical reduction of CO2 (CO2RR). However, less attention has been paid to developing Mn-SACs with nitrogen-free coordination environment for CO2 electroreduction. Herein, we construct a Mn SAC with a coordination structure of Mn-O4 anchored in nitrogen-doped graphitic carbon, which exhibits a 98.5 % of CO faradic efficiency (FECO) with a high CO partial current density (jCO) of ∼9.77 mA cm−2 at a low overpotential of 0.32 V in an H-type electrolytic cell. Furthermore, a higher current density of 27.8 mA cm−2 with a FECO of 93.8 % at 0.51 V overpotential was achieved in an ionic liquid (IL) electrolyte. Density functional theory (DFT) calculations reveal that the Mn-O4 site significantly lowers the free energy of the COOH* formation compared to the conventional N atoms coordinated Mn SACs, and thus facilitates the CO2-to-CO conversion.