Thiospinel NiCo₂S₄ Nanoflakes Grown on Ni Foam as Robust Electrocatalysts for Hydrogen Evolution in Alkaline Simulated Seawater

The hydrogen evolution reaction (HER) is a highly effective and environmentally sustainable approach for hydrogen generation enabled by electrocatalysts. In this study, NiCo 2 S 4 -based nanoflakes grown on Ni foam (NCS NF) were synthesized using a two-step hydrothermal method, involving the sulfidation of a NiCo precursor with Na 2 S. The resulting material, characterized by a nanoflake morphology and a cubic thiospinel crystal structure, provides an enhanced active surface area, facilitating efficient H + adsorption and promoting HER kinetics. Electrochemical testing reveals that NCS NF achieves a current density of 10 mA cm –2 at an overpotential of 106 mV in an alkaline electrolyte and 118 mV in a simulated seawater electrolyte, with corresponding Tafel slopes of 94 and 116 mV dec –1, respectively. Notably, the material exhibits stable HER activity in simulated seawater for up to 24 h with minimal degradation. These results demonstrate NCS NF as a highly efficient electrocatalyst for seawater splitting, presenting a promising candidate for large-scale hydrogen production.