Electronic asymmetry engineering of Fe–N–C electrocatalysts via second-shell coordination of B for boosting the oxygen reduction reaction

Abstract

Iron–nitrogen–carbon coordinated single-atom catalysts (Fe–N–C) stand out as particularly promising substitutes for traditional platinum-group metals for the oxygen reduction reaction (ORR). However, the symmetric distribution of electron density at the Fe–N₄ active sites leads to suboptimal adsorption of reaction intermediates, which limits intrinsic activity and stability. Herein we construct atomically dispersed Fe–N₄ moieties supported on B-doped carbon (Fe–N–B–C) with a stacked layer accordion structure by a one-step method. Benefiting from the disruption of their electronic symmetry via second-shell coordination of B, the intrinsic activity and stability of Fe–N₄ are improved. In addition, the carbon support, rich in mesopores and defects, enhances both mass and charge transfer within the Fe–N–B–C catalyst, thereby enhancing active site accessibility during the ORR. The Fe–N–B–C catalyst exhibits exceptional activity across a broad pH spectrum, with half-wave potentials (E_1/2) reaching 0.926 V in 0.1 M KOH and 0.798 V in 0.1 M HClO₄, respectively. The Zn–air battery (ZAB) employing Fe–N–B–C as the air cathode presents a maximum power density of 192 mW cm⁻² and ultra-high battery stability (>600 h) at 10 mA cm⁻².