Axial halogen coordinated metal-nitrogen-carbon moiety enables efficient electrochemical oxygen reduction to hydrogen peroxide

Human life relies on hydrogen peroxide (H2O2), which is a crucial chemical. H2O2 can be produced via elec-trochemical methods using two-electron oxygen reduction reaction (2e- ORR) on atomically dispersed catalysts, making it a promising substitute for the traditional anthraquinone process, but still has lenty of room for opti-mization. Axial coordination regulation of active sites is a potential means to improve the selectivity of 2e- ORR. Herein, we design twenty types of single atom sites with precisely defined M-N4-C moiety functionalized by axial coordination R (R=Cl, Br). By calculation of density functional theory (DFT), different from pristine M-N4-C moiety, Cl-Cu-N4 and Br-Zn-N4 especially Br-Zn-N4 has the most favorable 2e- ORR catalytic efficiency with the overpotential of 0.07 and 0.05 V, respectively. In addition, the Gibbs free energy of the intermediate O* exceeds 3.52 eV, indicating a significant suppression of the competitive 4e- ORR reaction. Electronic analyses show that the axial Br in Zn-N4-Br can optimize the 3D orbital of Zn center to enhance O2 adsorption and activation at Zn site, thus reducing ORR barrier and accelerating ORR kinetics. This work extends the field of view of adjusting the reaction path of monatomic electrocatalysis through axial coordination engineering.