Modifying electronic and physical properties of Fe-NSC catalyst for oxygen reduction reaction via sulfur doping process

Abstract

The primary challenge in the large-scale production of metal-air batteries or fuel cells is the high cost of Pt, which is used in the oxygen reduction reaction. To address this issue, we synthesized non-precious metal catalysts by doping Fe, N, and S in various sequences. X-ray diffraction and Raman spectroscopy proved that these catalysts had a higher degree of graphitization than carbon black. While the Fe3C phase was found in the catalyst without S, it was absent in all Fe-NSC catalysts. Imaging and X-ray absorption near edge structure (XANES) studies showed atomically dispersed Fe metal in the S-doped non-precious metal catalysts. X-ray photoelectron spectroscopy (XPS) and XANES reveal that the active site concentrations, inactive Fe-S bond, and oxidation number of the Fe species vary according to the N and S doping sequences. Fe-NSC-1 showed fast kinetics and high selectivity, with an onset potential of 0.96 V. Even after 10,000 potential cycles between 0.6 and 1.0 V, the half-wave potential for Fe-NSC-1 decreased by only 3%. Additionally, the Fe-NSC-1 catalyst showed a negligible decrease in current density during the methanol tolerance tests. Overall, this study found that the doping sequence plays a vital role in enhancing the electrochemical performance and stability of these catalysts under suitable operating conditions by influencing their chemical and electronic structures.