Tunable properties of WSe2 nanosheets and nano-dispersion via energy dependent exfoliation

Abstract

Transition metal dichalcogenides (TMDs) have emerged as promising electrocatalysts for various electrocatalytic processes. Molybdenum disulfide has been widely used, but a single electrocatalyst can hardly be applied to all reactions, making it essential to understand the electrochemistry of selected TMDs. Tungsten diselenide (WSe₂) is reactive in gas evolution processes, similar to molybdenum, yet has received limited attention. This work explores how different exfoliation powers affect WSe₂ structural configurations and their impact on catalytic performance in hydrogen evolution, oxygen evolution, and capacitive behaviour. The study investigates the structural properties of WSe₂ nanosheets in both liquid (dispersion) and solid (electrode) phases. Low exfoliation power (90.4 W) contributes to well-defined WSe₂, while higher power (814 W) leads to an increased number of selenium vacancies. These modifications influence key properties such as thickness, band gaps (1.518 to 1.578 eV), exfoliation yield (0.27 to 0.12 mg mL⁻¹), and oxide content (44.3% to 53.9%), resulting in distinct electrochemical behaviours in different electrolytes. WSe₂ nanosheets exfoliated at higher power exhibit reduced activity in the hydrogen evolution reaction (HER) due to the loss of W–Se bonds and the formation of an amorphous structure, but they show enhanced oxygen evolution reaction (OER) performance, particularly in alkaline media. Additionally, a higher concentration of selenium vacancies improves capacitive performance in acidic conditions due to proton contributions but are less favourable in neutral and basic electrolytes. This study highlights the importance of exfoliation power in tuning the structural properties of WSe₂ for specific electrochemical applications, advancing the understanding of its synthesis and performance.