Coupled Fe ₃ O ₄ ‐Cluster Precipitates and Single Fe‐Atom Catalysts Can Boost Oxygen Reduction via Concomitantly Accelerated Water Dissociation

Abstract

ABSTRACT Fe–N–C single‐atom catalysts (SACs) can deliver high activity for catalyzing the oxygen reduction reaction (ORR) in alkaline conditions. However, the sluggish water dissociation upon Fe–N 4 active sites limits their proton‐coupled electron transfer (PCET) capability, impeding their practical applications like anion‐exchange membrane fuel cells (AEMFCs). Here, inspired by the known nanoprecipitation behavior in solid‐solution alloys, a residual‐oxygen‐assisted precipitation strategy is undertaken to fabricate coupled Fe 3 O 4 ‐cluster precipitates along with single Fe‐atom catalysts (Fe 3 O 4 /Fe SA @NC), where Fe 3 O 4 clusters are generated by slight oxidation and local enrichment of Fe atoms in the Fe SA @NC matrix. Operando spectroscopy and theoretical calculations suggest that the Fe 3 O 4 ‐cluster precipitates not only induce asymmetric electronic structures of the Fe‐N 4 active center to optimize the OH* adsorption, but also accelerate the water dissociation on Fe‐N 4 sites to boost the PCET steps, thereby promoting the ORR. Notably, the coupled Fe 3 O 4 /Fe SA @NC exhibits superb alkaline ORR performance with a high half‐wave potential of 0.953 V versus RHE. When employed as cathode catalysts, the Fe 3 O 4 /Fe SA @NC demonstrates a high peak power density of 909.3 mW cm −2 and 219.4 mW cm −2 in AEMFCs and Zn‐air batteries, respectively, far exceeding that of the commercial Pt/C catalyst. The novel coupled metal‐oxide cluster/SAC strategy can be exploited as a generic approach for improving electrocatalytic performance.