Iron Nanoparticles Encapsulated in S,N-Codoped Carbon: Sulfur Doping Enriches Surface Electron Density and Enhances Electrocatalytic Activity towards Oxygen Reduction
2020
Development
of highly efficient nonprecious metal (NPM) catalysts
for oxygen reduction reaction (ORR) in acidic media is challenging
but of great significance. Herein, an effective ORR catalyst based
on Fe nanoparticles encapsulated by S,N-codoped few-layer defective
carbon (Fe@S,N-DC) was synthesized via a microwave-assisted strategy.
The obtained Fe@S,N-DC nanocomposite showed a remarkable electrocatalytic
activity toward ORR in acidic media, with a half-wave potential (E1/2) of +0.785 V versus reversible hydrogen
electrode, which was 80 mV more positive than that of the sulfur-free
counterpart (Fe@N-DC). Furthermore, due to the protection by the S,N-codoped
carbon shell, the Fe@S,N-DC nanocomposite displayed apparent stability
with only a 13 mV negative shift of E1/2 after 10,000 cycles and excellent tolerance to methanol. X-ray absorption
near-edge spectroscopy measurements confirmed the formation of multiple
defective sites on the S,N-codoped carbon surface and strong interfacial
electron transfer from the Fe core to the outer carbon surface, as
compared to the sulfur-free counterpart. The enriched electron density
on the defective carbon surface of Fe@S,N-DC, induced by the interfacial
electron transfer, facilitated the reduction of O2 to OOH*,
leading to enhanced ORR performance. These results shed light on the
significance of S doping in Fe–N–C catalysts in the
design of high-performance NPM catalysts for ORR in acidic media.
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