Effect of a sulfur and nitrogen dual-doped Fe–N–S electrocatalyst for the oxygen reduction reaction

Herein, we report the synthesis of a non-precious metal dual-doped catalyst. Melamine and lipoic acid were used as precursors for the nitrogen and sulfur dopant atoms, respectively, which were mixed with iron precursors and carbon black and pyrolyzed at 700 °C to yield the catalyst Fe-M-LA/C. Fe-M-LA/C shows high oxygen reduction reaction (ORR) capability, with an almost-ideal electron transfer number of 3.99. It shows almost no degradation after potential cycling for 30 000 cycles, and the structural analysis indicates that a graphene-like structure of Fe-M-LA/C can improve its ORR activity, electrical conductivity, and corrosion resistance. X-ray photoelectron spectroscopy (XPS) results show that the catalyst has high contents of pyridinic- and quaternary N atoms and thiophene S atoms that can significantly enhance the ORR performance of Fe-M-LA/C. X-ray absorption spectroscopy (XAS) data show that the oxidation state of iron and the interatomic distance of the heteroatoms in Fe-M-LA/C play an important role in determining the ORR ability. These data confirm that the presence of a nitrogen and sulfur dual-doped –Fe–N–S– structure can enhance the ORR kinetics.