Planar Chlorination Engineering: A Strategy of Completely Breaking the Geometric Symmetry of Fe‐N₄ Site for Boosting Oxygen Electroreduction

Abstract Introducing asymmetric elements and breaking the geometric symmetry of traditional metal‐N₄ site for boosting oxygen reduction reaction (ORR) are meaningful and challenging. Herein, the planar chlorination engineering of Fe‐N₄ site is first proposed for remarkably improving the ORR activity. The Fe‐N₄/CNCl catalyst with broken symmetry exhibits a half‐wave potential (E_1/2) of 0.917 V versus RHE, 49 and 72 mV higher than those of traditional Fe‐N₄/CN and commercial 20 wt% Pt/C catalysts. The Fe‐N₄/CNCl catalyst also has excellent stability for 25 000 cycles and good methanol tolerance ability. For Zn‐air battery test, the Fe‐N₄/CNCl catalyst has the maximum power density of 228 mW cm⁻² and outstanding stability during 150 h charge–discharge test, as the promising substitute of Pt‐based catalysts in energy storage and conversion devices. The density functional theory calculation demonstrates that the adjacent C─Cl bond effectively breaks the symmetry of Fe‐N₄ site, downward shifts the d‐band center of Fe, facilitates the reduction and release of OH^*, and remarkably lowers the energy barrier of rate‐determining step. This work reveals the enormous potential of planar chlorination engineering for boosting the ORR activity of traditional metal‐N₄ site by thoroughly breaking their geometric symmetry.