Engineering Atomic Single Metal-FeN₄Cl Sites with Enhanced Oxygen-Reduction Activity for High-Performance Proton Exchange Membrane Fuel Cells

Fe-N-C single-atomic metal site catalysts (SACs) have garnered tremendous interest in the oxygen reduction reaction (ORR) to substitute Pt-based catalysts in proton exchange membrane fuel cells. Nowadays, efforts have been devoted to modulating the electronic structure of metal single-atomic sites for enhancing the catalytic activities of Fe-N-C SACs, like doping heteroatoms to modulate the electronic structure of the Fe-N_xactive center. However, most strategies use uncontrolled long-range interactions with heteroatoms on the Fe-N_xsubstrate, and thus the effect may not precisely control near-range coordinated interactions. Herein, the chlorine (Cl) is used to adjust the Fe-N_xactive center via a near-range coordinated interaction. The synthesized FeN₄Cl SAC likely contains the FeN₄Cl active sites in the carbon matrix. The additional Fe-Cl coordination improves the instrinsic ORR activity compared with normal FeN_xSAC, evidenced by density functional theory calculations, the measured ORR half-wave potential (E_1/2, 0.818 V), and excellent membrane electrode assembly performance.