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 (NaBH(4)) 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 × 10(20) 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 O(2) 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 H(2)-O(2) conditions at 80 °C, demonstrating its potential for fuel cell applications.