Free-standing S, N co-doped graphene/Ni foam as highly efficient and stable electrocatalyst for oxygen evolution reaction

Three-dimensional S, N co-doped graphene/Ni foam (3DSNG/NF) hybrid electrocatalyst for oxygen evolution reaction (OER) is presented and prepared by a facile chemical vapor deposition (CVD). The doping concentrations of N and S of 3DSNG can be easily modulated by growth parameters, which strongly influence its catalytic activity. As a free-standing hybrid electrocatalyst without polymer binder, the optimized 3DSNG/NF doped with 2.56 at% N and 2.95 at% S, delivers good catalytic activity: it shows a very low Tafel slope of 45.61 mV dec−1 in alkaline solution, which is much lower than that of RuO2 (78.62 mV dec−1); it requires only a very low overpotential of 339 mV to obtain a large current density of 100 mA cm−2, which is far lower than that of RuO2 (418 mV); furthermore, it exhibits good long-term stability even after 50-h current-time test. The good OER performance and stability of 3DSNG/NF can be attributed to the synergistic effects originating from its unique hierarchical architecture. The porous and conductive graphene skeleton can not only guarantee the mechanical and structural stability, but also facilitate the electron transfer and ion diffusion; most important, the homogenously doped nitrogen and sulfur atoms create abundant catalytic active sites.