N-doped graphene encapsulated FeNi core–shell with S defects for the oxygen evolution reaction

Abstract

The synergistic effect between the transition metal sulfide alloy core, the N-doped graphene shell, and the internal interfacial potential serves to regulate the electronic structure and facilitate electron transfer. We used Fe-based Prussian blue analogues as a single precursor to prepare a N-doped graphene-coated metal core–shell structure (FeNi@NG) through hydrothermal and high-temperature solid phase reactions. The S source was then introduced and annealed, yielding a S, N co-doped graphene-encapsulated metal core–shell structure (FeNi–S@NG). Finally, a nitrogen-doped graphene-coated metal core–shell structure with S defects (S–FeNi@NG) was obtained through NaBH₄ liquid-phase reduction. The synergistic effect between the transition metal sulfide alloy core and the N-doped graphene shell, in conjunction with the internal interfacial potential regulate the electronic structure and facilitate electron transfer. Numerous sulfur vacancies accelerate electron transfer and enhance OER catalytic performance. The optimized material, S–FeNi@NG, exhibited excellent OER catalytic performance, with an overpotential of 250 mV (at 10 mA cm⁻²) and a Tafel slope of 90.95 mV dec⁻¹ in an alkaline electrolyte.