Optimizing reaction intermediate adsorption by engineering the coordination structure of single-atom Fe–N5–C electrocatalysts for efficient oxygen reduction

Abstract

Optimizing the adsorption energy of intermediates by precisely modulating the coordination structure of single-atom M–N_x–C electrocatalysts to significantly improve the oxygen reduction reaction (ORR) performance still remains a great challenge. In this work, guided by density functional theory (DFT) calculations, an axial coordination FeN₅ single-atom catalyst was constructed by way of an FeN₄ species anchored with the N atom from nitrogen-doped graphene to promote the ORR catalytic performance. The special coordination structure of FeN₅ can significantly optimize the adsorption of the reaction intermediate and reduce the overpotential of the ORR process compared to that of the FeN₄ planar structure, which is commonly used. Hence, the constructed axial coordination FeN₅ single-atom catalyst shows extraordinary ORR catalytic performance (E_onset/E_half-wave = 0.992/0.916 V vs. reversible hydrogen electrode (RHE), J_L = 6.06 mA cm⁻² and a 93.9% current retention after 15 h) and a maximum power density of 141 mW cm⁻² in a zinc–air battery, which is superior to those of commercial Pt/C. These findings provide new insights into the construction of high-efficiency ORR catalysts from the design of a single atom coordination environment.