Single transition metal atom-doped graphene supported on a nickel substrate: Enhanced oxygen reduction reactions modulated by electron coupling

Single transition metal (TM) atom-doped graphene has been experimentally proved to be effective for catalyzing electrochemical reactions. However, oxygen reduction reactions (ORR) exhibit poor catalytic performance due to the high binding energy between the active site and the adsorbed species. Here, we propose a feasible strategy to modulate the binding strength of the oxygenated species on the graphitic nanosheet by introducing metal substrate gating. Density functional theory calculation results reveal the remarkable enhancement of ORR performance with the confinement of the Ni(111) surface, and the overpotentials for six different transition metal (TM) atom-doped pentagon|octagon|pentagon (5|8|5) graphene (TM@5|8|5G) systems on the Ni(111) surface can be significantly reduced, particularly for the case of Co@5|8|5G (from 0.98 to 0.33 V). This is mainly attributed to the electron coupling between the metal substrate and TM@5|8|5G. Moreover, the catalytic activity can be well modulated by adjusting d-band centers of TM atoms, leading to an ideal energy level of the d-band center for TM@5|8|5G on the Ni substrate (−1.48 eV), at which ORR can achieve the highest performance