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

Abstract

AbstractIntroducing 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 (E1/2) 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.