Tip-like Fe-N₄ Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction

Single atom catalysts with defined local structures and favorable surface microenvironments are significant for overcoming slow kinetics and accelerating O₂ electroreduction. Here, enriched tip-like FeN₄ sites (T-Fe SAC) on spherical carbon surfaces were developed to investigate the change in surface microenvironments and catalysis behavior. Finite element method (FEM) simulations, together with experiments, indicate the strong local electric field of the tip-like FeN₄ and the more denser interfacial water layer, thereby enhancing the kinetics of the proton-coupled electron transfer process. In situ spectroelectrochemical studies and the density functional theory (DFT) calculation results indicate the pathway transition on the tip-like FeN₄ sites, promoting the dissociation of O-O bond via side-on adsorption model. The adsorbed OH* can be facilely released on the curved surface and accelerate the oxygen reduction reaction (ORR) kinetics. The obtained T-Fe SAC nanoreactor exhibits excellent ORR activities (E_1/2 =0.91 V vs. RHE) and remarkable stability, exceeding those of flat FeN₄ and Pt/C. This work clarified the in-depth insights into the origin of catalytic activity of tip-like FeN₄ sites and held great promise in industrial catalysis, electrochemical energy storage, and many other fields.