Edge-Site Engineering of Atomically Dispersed Fe-N4 by Selective C-N Bond Cleavage for Enhanced Oxygen Reduction Reaction Activities

Single-atom metal-nitrogen-carbon (M-N-C) catalysts have sparked intense interests, but the catalytic contribution of N-bonding environment neighboring M-N-4 sites lacks attention. Herein, a series of Fe-N-C nanoarchitectures have been prepared, which confer adjustable numbers of atomically dispersed Fe-N-4 sites, tunable hierarchical micro-mesoporous structures and intensified exposure of interior active sites. The optimization between Fe-N-4 single sites and carbon matrix delivers superior oxygen reduction reaction activity (half-wave potential of 0.915 V vs RHE in alkaline medium) with remarkable stability and high atom-utilization efficiency (almost 10-fold enhancement). Both experiments and theoretical calculations verified the selective C-N bond cleavage adjacent to Fe center induced by porosity engineering could form edge-hosted Fe-N-4 moieties, and therefore lower the overall oxygen reduction reaction barriers comparing to intact atomic configuration. These findings provide a new pathway for the integrated engineering of geometric and electronic structures of single-atom materials to improve their catalytic performance.