The Role Of Sulfur Doping In Determining The Performance Of Fe/N-C Based Electrocatalysts For Oxygen Reduction Reactions

The effect of S-doping on the performance of Fe/N-C catalysts for ORR was studied. It was found that the abundant C-S-C bonds in the sulfur-doped catalysts enhanced the ORR activity greatly, while the existence of excessive C-SOX-C bonds was adverse to the kinetics of ORR. Also, the existence of Fe was able to increase the contents of both C-S-C bond and graphite N during the pyrolysis stage of preparation, thus generating more ORR active sites. The resulted effective configurations of S (C-S-C) and active N (both graphitic N and pyridinic N), and the combination of rich hierarchical porous structure with the encased Fe3C nanoparticles were responsible for the excellent performance of catalysts. Specifically, the E-1/2 of the prepared FeNSC-10S catalyst reached 0.91 V in a 0.1 M KOH electrolyte solution, which was 20 mV positive shift to the E-1/2 of the 20 wt.% Pt/C commercial catalyst. The electron transfer number was determined to be 3.85-3.91 over the potential range of 0.4-0.8 V, indicating that the ORR catalytic process proceeded in a reaction pathway with nearly 4e(-) transfer. The developed catalyst also demonstrated a long-term stability as well as a superior methanol tolerance in alkaline conditions.