Theoretical investigation on catalytic mechanisms of oxygen reduction and carbon monoxide oxidation on the MnNx system

Abstract

Single-atom catalysts (SACs) have been extensively studied due to their highly dispersed atomic levels, which greatly improve the distribution of active sites and maximum utilization of the catalyst. In this study, Mn-based SACs were modeled on N-doped graphene with single and double vacancy defects, and 11 types of MnN_x models containing various three- and four-coordinate structures were considered. The ORR overpotential of MnN₃ (MnN₄) was lowest in the three-coordinate structure (four-coordinate structure), which was selected to study catalytic activities for the oxygen reduction reaction (ORR) and reaction mechanism. The best reaction path for ORR on MnN₄ is *O₂ → *O + H₂O → *OH → H₂O and the energy barrier of the rate-determining step (RDS) is 0.172 eV. According to the adsorption energy competition, the best catalytic performance of MnN₄ was selected to study the various reaction mechanisms of carbon monoxide oxidation (COOR). The best reaction path is the CO oxidation on MnN₄ along the termolecular Eley–Rideal (TER) with a RDS energy barrier of 0.218 eV. These results suggest that MnN₄ is a promising bifunctional catalyst.