Regulating the Electronic Configuration of Single-Atom Catalysts with Fe-N5 Sites via Environmental Sulfur Atom Doping for an Enhanced Oxygen Reduction Reaction

Heteroatom doping is considered an essential strategy to modulate the Fe-N-C catalytic activity for the oxygen reduction reaction (ORR) in energy conversion technologies. However, challenges remain in achieving a singular form of heteroatom doping, i.e., asymmetrical coordination with metal sites and heteroatom doping in environmental skeleton carbons. And a low doping efficiency and inappropriate doping ratios result in the excessive use of heteroatom-containing organic additives, further limiting the achievement of sustainability. In this work, we prepared an atom-economical Fe-N-5 single-atom catalyst (SAC) with only environmental S atom doping, which was synthesized by pyrolyzing an axial imidazole-coordinated thiophene iron porphyrin precursor on PVI-functionalized carbon black. Due to the electron-donating properties of thiophene-S atoms, the intrinsic activity of the Fe-N-5 site was significantly promoted by regulating the electronic configuration through the long-range interaction, thus lowering the energy barrier of the ORR. As expected, the resultant catalyst exhibited an efficient ORR activity in alkaline media and in the aqueous zinc-air battery, with a higher half-wave potential of 0.89 V vs RHE and a maximum power density of 147 mW cm(-2) than those of 20 wt % Pt/C (E-1/2 = 0.87 V, P-max = 120 mW cm(-2)). This work provides a facile heteroatom-doping engineering approach to boost the intrinsic catalytic activity of advanced SACs in energy conversion applications.