One-step electrodeposition of a hierarchically structured S-doped NiCo film as a highly-efficient electrocatalyst for the hydrogen evolution reaction

An enormous challenge in the development of renewable hydrogen sources for electricity-driven water-splitting systems has been the limitation of the earth-abundant and robust highly-active cathode electrocatalysts. In this work, we developed a simple sulfur-anion doping strategy to obtain the S-doped NiCo composite (S-NiCo@50) on Ni foam (NF) via a one-step electrochemical deposition. It was found that doped sulfur plays a crucial role in reducing the overpotential of hydrogen evolution by providing abundant active sites as identified by the XPS spectrum. The formed metallic Ni and Co effectively promoted electron transportation. The synergistic effects between the amorphous CoxNiyS(x+y) substance and crystalline Ni and Co metal seemed to result in enhanced HER activity. In particular, the S-NiCo@50 electrode, featuring a hierarchical morphology, showed an ultralow overpotential of 28 and 125 mV at 10 and 100 mA cm-2, respectively, in 1.0 M NaOH with a large exchange current density (j0) of 4.8 mA cm-2 as well as high conductivity and stability; its catalytic properties are superior to most of the reported alkaline electrocatalysts and are on par with commercial Pt/C. Assembled with the counter electrode (Ni-Fe/NF), the overall water splitting was proved with a low 1.55 V at 10 mA cm-2. Moreover, we built the Ni24Co6S6 cluster as the S-NiCo@50 model and revealed its intrinsic activity by density functional theory (DFT) calculations. This study shows that S-doping and component control can be an exquisite strategy for realizing high-efficiency electrochemical water reduction.