Axial modulation of Fe sites realizing high-performance oxygen reduction reaction of FeN4 catalysts

Abstract

The modulation of the microenvironment of Fe–N–C conventional catalysts is considered a feasible strategy to improve the catalytic performance. Herein, we report the synthesis of Fe single-atom catalysts with S (axially oriented) and N (horizontally oriented) coordination modes in a MOF-derived hierarchical porous carbon (Fe-N₄S₁). High oxygen reduction reaction (ORR) activity with a half-wave potential of 0.88 V has been realized. In addition, we found using density functional theory calculations (DFT) that the introduction of axial S atoms around Fe single atoms can redistribute the d-band electrons of Fe compared with a conventional FeN₄ catalyst. This leads to a more deviation of the d-band center from the Fermi energy level, thus weakening its intermediate adsorption behavior, maintaining the advantages of high catalytic activity of FeN₄ and solving the drawbacks of conventional FeN₄ catalysts with strong adsorption to intermediates. Our findings provide a new idea for the microenvironmental modulation of single-atom catalysts, which can realize controllable electron distribution of single atoms.