Sub-50 nm Iron–Nitrogen-Doped Hollow Carbon Sphere-Encapsulated Iron Carbide Nanoparticles as Efficient Oxygen Reduction Catalysts

Sub-50 nm iron–nitrogen-doped hollow carbon sphere-encapsulated iron carbide nanoparticles (Fe₃C-Fe,N/C) are synthesized by using a triblock copolymer of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) as a soft template. Their typical features, including a large surface area (879.5 m² g⁻¹), small hollow size (≈16 nm), and nitrogen-doped mesoporous carbon shell, and encapsulated Fe₃C nanoparticles generate a highly active oxygen reduction reaction (ORR) performance. Fe₃C-Fe,N/C hollow spheres exhibit an ORR performance comparable to that of commercially available 20 wt% Pt/C in alkaline electrolyte, with a similar half-wave potential, an electron transfer number close to 4, and lower H₂O₂ yield of less than 5%. It also shows noticeable ORR catalytic activity under acidic conditions, with a high half-wave potential of 0.714 V, which is only 59 mV lower than that of 20 wt% Pt/C. Moreover, Fe₃C-Fe,N/C has remarkable long-term durability and tolerance to methanol poisoning, exceeding Pt/C regardless of the electrolyte.