Dual-function synergy in boron-doped Fe–N–C: enhanced site density and intrinsic activity

Abstract

Atomically dispersed transition metal, nitrogen co-doped carbon (M–N–C) is hailed as the most promising platinum alternative for the oxygen reduction reaction (ORR); however, its practical deployment is bottlenecked by inferior intrinsic activity and insufficient site density. Herein, we report a sodium borohydride (NaBH₄) assisted synthesis strategy to achieve dual enhancement of active site density and intrinsic activity. This strategy endows a B-doped catalyst (denoted as Fe–sZ8–N–C) with a high active site density of 2.26 × 10²⁰ sites per g, a two-fold enhancement over conventional Fe–N–C. Besides, the intrinsic activity of the catalyst is improved from 0.96 e per site per s to 1.5 e per site per s. Density functional theory (DFT) calculations reveal that the boron-modulated coordination structure switches the ORR pathway from associative OOH dissociation to direct O₂ cleavage while weakening intermediate adsorption strength, thereby boosting intrinsic activity. When assembled in practical PEMFC devices, the optimized Fe–sZ8–N–C catalyst delivers an exceptional peak power density of 1.3 W cm⁻² under H₂–O₂ conditions at 80 °C, demonstrating its potential for fuel cell applications.