Green synthesis of ultrathin WS2 nanosheets for efficient hydrogen evolution reaction†

Abstract

Transition metal dichalcogenide (TMD) nanostructures have emerged as promising electrocatalysts for the hydrogen evolution reaction (HER) as there is an increasing demand for cost-effective and sustainable hydrogen production. Despite significant progress, there is still a critical need for developing facile and green methods for synthesizing ultrathin TMD nanostructures. In this study, we introduce a green, top-down synthesis method to produce highly exfoliated WS₂ nanosheets. The process combines the ultrasonication of bulk WS₂ in a binary water–ethanol solvent with a solvothermal treatment. The resulting ultrathin WS₂ nanosheets exhibit clean surfaces free of surface ligands and impurities, high crystallinity in the semiconducting hexagonal phase, and outstanding electrochemical activity for HER. Key performance metrics include a low onset potential of −0.32 V (vs. reversible hydrogen electrode (RHE)) at 10 mA cm⁻² and a low Tafel slope of 160 mV dec⁻¹ with a catalyst loading of 0.76 mg cm⁻². The promising HER performance is attributed to (1) a high density of exposed edges and defects, (2) enhanced charge transport due to high crystallinity, and (3) clean surfaces enabling efficient interfacial electron transfer. Furthermore, operando Raman spectroscopy using a 3D-printed electrochemical cell identifies the catalytically active sites on WS₂ nanosheets for HER. This work provides a green route to high-performance, low-dimensional electrocatalysts for sustainable hydrogen production.