Investigations into transition metal dichalcogenides for electrocatalysis

Transition metal dichalcogenides have emerged as promising candidates for the hydrogen evolution reaction (HER) due to their unique properties and low costs compared to platinum-group metals (PGMs). Despite recent advancements, there is still a gap in reporting the electrochemical rate constants and detailed kinetics for improved HER activity due to transition metal dichalcogenides (TMDs) as well as the potential effects of mixing various TMDs for enhanced HER performance. This study investigated the HER electrocatalytic activity of TMDs as well as novel strategies for enhancing their catalytic activity and determining the reaction kinetics. Different structural morphologies (bulk and nanoparticle) of one TMD, MoS\(_2\), were investigated to ascertain how it affects HER electrocatalytic activity. The impact electrochemistry technique was incorporated to study the nanoparticulate forms. The MoS\(_2\) nanoparticles registered an improved onset potential of -0.10 V (vs RHE) through impact electrochemistry compared to 0.29 V (vs RHE) of the bulk MoS\(_2\) for HER. TMD heterostructures were also investigated, and they were synthesized using a method distinct from those that have been reported in the literature. Two methods were employed to create the heterolayers: utilising a drop-cast nanoparticle layer and an electrodeposited film. The heterolayers were evaluated for HER, and the heterostructures with an overlay of MoS\(_2\) displayed superior stability compared to those with an overlay of MoSe\(_2\). The stable heterolayers registered standard electrochemical rate constants (k0) of (3.20 ± 0.10) × 10\(^{-4}\) cm s\(^{-1}\) and (1.73 ± 0.03) × 10\(^{-4}\) cm s\(^{-1}\) for WS\(_2\)/MoS\(_2\) and MoSe\(_2\)/MoS\(_2\) respectively, which was an overall improvement compared to reported rate constants for electrodeposited MoS\(_2\). After evaluating the heterolayers, a novel mechanochemical approach was used to synthesize binary and ternary mixtures of TMDs to enhance the catalytic activity of the resulting hybrids. Electrochemical testing of the hybrids for HER exhibited improved HER performance in terms of onset potential and electrochemical rate constants compared to the individual TMDs. These ranged from 0.52 × 10\(^{-3}\) cm s\(^{-1}\) to 8.2 × 10\(^{-3\) cm s\(^{-1}\), with hybrids containing selenium having higher electrochemical rate constants. This improvement was due to the increased active sites, the exfoliation of the TMDs that generated 1T-monolayer components known for their higher activity in HER, and the combined effect of mixing two or more catalytically active materials.