Nitrogen, sulfur co-doped carbon embedded with iron nanoparticles as an efficient oxygen reduction electrocatalyst

Abstract

In this work, N, S co-doped carbon embedded with Fe nanoparticles (Fe/NSC) used as an effective electrocatalyst for oxygen reduction reaction (ORR) is synthesized by a two-step copyrolysis of cheap and available high‑sulfur coal with KOH, then a trace amount of FeCl3. The as-prepared Fe/NSC exhibits an improved ORR electrocatalytic activity than NSC (high‑sulfur coal derived N, S co-doped carbon) and coal-Fe (direct copyrolysis high‑sulfur coal with FeCl3) in terms of the ORR peak potential, half-wave potential, limiting-diffusion current density, a main 4-electron reaction pathway and low Tafel slope in 0.1 M KOH evaluated by electrochemical measurements. Structural characterizations by TEM-mappings and XRD indicate that Fe/NSC has an amorphous carbon structure coupled with heteroatoms N and S distributed uniformly and Fe nanoparticles. Raman and XPS results indicte that Fe/NSC has less defect, and the addition of Fe nanoparticles in Fe/NSC leads to a decreased level of N and S retention as compared with NSC. Role of metallic Fe nanoparticles in ORR electrocatalytic performance is also clarified by acid leaching. This two-step copyrolysis process is also a promising route for sustainable utilization of high‑sulfur coal.