Axial Chlorine Induced Electron Delocalization in Atomically Dispersed FeN4 Electrocatalyst for Oxygen Reduction Reaction with Improved Hydrogen Peroxide Tolerance

Abstract Atomically dispersed iron sites on nitrogen‐doped carbon (Fe‐NC) are the most active Pt‐group‐metal‐free catalysts for oxygen reduction reaction (ORR). However, due to oxidative corrosion and the Fenton reaction, Fe‐NC catalysts are insufficiently active and stable. Herein, w e demonstrated that the axial Cl‐modified Fe‐NC (Cl‐Fe‐NC) electrocatalyst is active and stable for the ORR in acidic conditions with high H2O2 tolerance. The Cl‐Fe‐NC exhibits excellent ORR activity, with a high half‐wave potential (E1/2) of 0.82 V versus a reversible hydrogen electrode (RHE), comparable to Pt/C (E1/2 = 0.85 V versus RHE) and better than Fe‐NC (E1/2 = 0.79 V versus RHE). X‐ray absorption spectroscopy analysis confirms that chlorine is axially integrated into the FeN4. More interestingly, compared to Fe‐NC, the Fenton reaction is markedly suppressed in Cl‐Fe‐NC. In situ electrochemical impedance spectroscopy reveals that Cl‐Fe‐NC provides efficient electron transfer and faster reaction kinetics than Fe‐NC. Density functional theory calculations reveal that incorporating Cl into FeN4 can drive the electron density delocalization of the FeN4 site, leading to a moderate adsorption free energy of OH* (∆GOH*), d‐band center, and a high onset potential, and promotes the direct four‐electron‐transfer ORR with weak H2O2 binding ability compared to Cl‐free FeN4, indicating superior intrinsic ORR activity.