A high-density nickel-cobalt alloy embedded in nitrogen-doped carbon nanosheets for the hydrogen evolution reaction

The development of novel non-noble electrocatalysts is critical for an efficient electrochemical hydrogen evolution reaction (HER). In this study, high-density nickel-cobalt alloy nanoparticles embedded in the bent nitrogen-doped carbon nanosheets are prepared as a high-performance catalyst. The optimized Ni₇Co₃/NC-500 catalyst displays quite a low overpotential of 90 mV at a current density of 10 mA cm^-2, and a small Tafel slope of 64 mV dec^-1 in alkaline medium, and even performs better than commercial 20% Pt/C at a high current density (η₁₅₀ = 233 mV for Ni₇Co₃/NC-500 and η₁₅₀ = 267 mV for 20% Pt/C). Specifically, the high-density nickel-cobalt alloy (with an average size of 6.2 nm and a distance of <3.0 nm) embedded in the bent carbon nanosheets provides plentiful active sites. Furthermore, in situ visualization of the produced hydrogen bubbles shows that the small size of hydrogen bubbles (d = 0.2 mm for Ni₇Co₃/NC-500 vs. d = 0.8 mm for 20% Pt/C) resulting from the small water contact angle and the bent nanosheet structure would inhibit the aggregation of H₂ bubbles on the surface to facilitate efficient mass diffusion. Density functional theory calculations reveal that the formation of the nickel-cobalt alloy can effectively lower water dissociation energy barriers and optimize hydrogen adsorption Gibbs free energy, manifesting a high HER activity.