Time-Dependent Oxidative Degradation of WSe2 Nanosheets and Its Influence on HER Catalysis

The selection of an appropriate solvent has long been a critical factor in the liquid phase exfoliation (LPE) of two-dimensional transition metal dichalcogenide (2D TMD) nanosheets. N-methyl-2-pyrrolidone (NMP) remains one of the most commonly used solvents due to its favourable surface tension compatibility, particularly with tungsten diselenide (WSe2), which facilitates a relatively high yield of exfoliated nanosheets. However, prolonged exposure of the nanosheets to NMP promotes oxidation, consequently diminishing their hydrogen evolution reaction (HER) activity. In contrast, a more environmentally friendly solvent system, consisting of isopropyl alcohol (IPA) and deionised water (DI), induces significantly less oxidation and results in enhanced HER performance. Notably, this green solvent system achieves the lowest overpotential of 0.209 V vs RHE after 24 hours of chronoamperometry.