Planar Chlorination Engineering: A Strategy of Completely Breaking the Geometric Symmetry of Fe-N 4 Site for Boosting Oxygen Electroreduction.

Introducing asymmetric elements and breaking the geometric symmetry of traditional metal-N 4 site for boosting oxygen reduction reaction (ORR) are meaningful and challenging. Herein, the planar chlorination engineering of Fe-N 4 site was firstly proposed for remarkably improving the ORR activity. The Fe-N 4 /CNCl catalyst with broken symmetry exhibited a half-wave potential (E 1/2 ) of 0.917 V versus RHE, 49 mV and 72 mV higher than those of traditional Fe-N 4 /CN and commercial 20 wt% Pt/C catalysts. The Fe-N 4 /CNCl catalyst also had excellent stability for 25,000 cycles and good methanol tolerance ability. For Zn-air battery test, the Fe-N 4 /CNCl catalyst had 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 demonstrated the adjacent C-Cl bond effectively broke the symmetry of Fe-N 4 site, downward shifted the d-band center of Fe, facilitated the reduction and release of OH * , and remarkably lower the energy barrier of rate-determining step. This work revealed the enormous potentials of planar chlorination engineering for boosting the ORR activity of traditional metal-N 4 site by thoroughly breaking their geometric symmetry. This article is protected by copyright. All rights reserved.