Tandem NiO–Ni(OH)2/VS2 nanosheets: a robust photocatalyst for hydrogen evolution†

The utilization of hydrogen as a sustainable alternative to fossil fuels is gaining momentum due to its environmental compatibility and recyclability. In this study, we present a novel approach employing a NiO–Ni(OH)₂ hybrid decorated on VS₂ nanosheets, synthesized through a facile one-pot hydrothermal method, for enhancing the photocatalytic activity in the hydrogen evolution reaction (HER) from a methanol–water mixture under visible light irradiation. The synthesized samples underwent comprehensive characterization via XRD, FT-IR, SEM, TEM, XPS, BET, optical bandgap determination, and electrochemical analyses including CV, LSV, Tafel slope, and EIS Nyquist plot. Characterization results revealed that the presence of a minor quantity of NiO–Ni(OH)₂ effectively restrained the growth of VS₂ crystallites, leading to a reduction in average crystallite size with increasing NiO–Ni(OH)₂ content. XPS analysis confirmed the presence of NiO–Ni(OH)₂ on VS₂ and the oxidation states of V⁴⁺ and Ni²⁺ cations. Notably, the photocatalytic experiments demonstrated that NiO–Ni(OH)₂ served as an excellent co-catalyst for enhancing H₂ production over VS₂, with the H₂ production rate of 41642.2 μmol g⁻¹ h⁻¹ achieved with a loading of 0.8 mol% of NiO–Ni(OH)₂ to VS₂, surpassing the pristine VS₂ by over fourfold. The enhanced H₂ production activity was attributed to the accumulation of NiO–Ni(OH)₂ particles on the VS₂ surface, facilitating efficient movement of photoexcitons and minimizing photogenerated electron–hole pair recombination, thereby reducing hydrogen production overpotential and enhancing catalytic hydrogen generation. The outstanding performance and durability of the NiO–Ni(OH)₂/VS₂ photocatalyst suggest its potential as a cost-effective and promising candidate for hydrogen evolution reaction photocatalysis.