The Effect of N-Defect and Axial Halogen Atom on Electrocatalytic Oxygen Reduction Reaction Activity of FeN₄ Single-Atom Catalysts: A Density Functional Theory Study

Single atom catalysts had been widely used in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). However, the relationship between local coordination environment and catalytic activity were unclear. In this work, the effect of N-defect and axial halogen atoms on electrocatalytic OER/ORR activity of FeN4 catalysts were investigated by density functional theory calculations (DFT). When the overpotential was the only criterion, FeN3Br was the optimal candidates for OER, followed by FeN3F, FeN4I, FeN4Cl and FeN4Br; FeN4I, FeN4Br and FeN4Cl were also the promising candidates for ORR. FeN4I, FeN4Br and FeN4Cl may be excellent ORR catalysts in an acidic media because of the low overpotential and reaction barrier of kinetics rate limiting step. In summary, N-defect and axial halogen atoms can effectively balance kinetics, thermodynamics and catalytic activity.