In situ Activation of Molecular Oxygen at Intermetallic Spacing‐Optimized Iron Network‐Like Sites for Boosting Electrocatalytic Oxygen Reduction

Abstract

AbstractThe oxygen reduction reaction (ORR) catalyzed by transition‐metal single‐atom catalysts (SACs) is promising for practical applications in energy‐conversion devices, but great challenges still remain due to the sluggish kinetics of O═O cleavage. Herein, a kind of high‐density iron network‐like sites catalysts are constructed with optimized intermetallic distances on an amino‐functionalized carbon matrix (Fe‐HDNSs). Quasi‐in situ soft X‐ray absorption spectroscopy and in situ synchrotron infrared characterizations demonstrate that the optimized intermetallic distances in Fe‐HDNSs can in situ activate the molecular oxygen by fast electron compensation through the hybridized Fe 3d‒O 2p, which efficiently facilitates the cleavage of the O═O bond to *O species and highly suppresses the side reactions for an accelerated kinetics of the 4e− ORR. As a result, the well‐designed Fe‐HDNSs catalysts exhibit superior performances with a half‐wave potential of 0.89 V versus reversible hydrogen electrode (RHE) and a kinetic current density of 72 mA cm−2@0.80 V versus RHE, exceeding most of the noble‐metal‐free ORR catalysts. This work offers some new insights into the understanding of 4e− ORR kinetics and reaction pathways to boost electrochemical performances of SACs.