Electrocatalysis of layered Group 5 metallic transition metal dichalcogenides (MX2, M = V, Nb, and Ta; X = S, Se, and Te)
The revelation of MoS2 as an efficient electrocatalyst for the hydrogen evolution reaction (HER) has ratcheted up interest in other transition metal dichalcogenides (TMDs). To date, extensive studies have been focused towards semiconducting Group 6 TMDs while research into metallic Group 5 TMDs has been comparatively limited. Past computational screening of Group 5 TMDs showed propitious Gibbs free energy of the adsorbed hydrogen (DGH) for HER, especially for VS2, which prompted us to experimentally explore their HER efficiency. In addition to the HER electrocatalytic performance, we examine the inherent electrochemistry and the charge-transfer property of the entire set of Group 5 TMDs in the bulk form: VS2, VSe2, VTe2, NbS2, NbSe2, NbTe2, TaS2, TaSe2 and TaTe2. We demonstrate that the nine Group 5 TMDs show distinctive inherent electroactivities arising from their intrinsic electrochemical processes or surface oxides. TaS2 possesses the fastest heterogeneous electron transfer (HET) rate at 3.4 x 10(-3) cm s(-1) amongst the Group 5 TMDs and may be ideal for electrochemical sensing. Chalcogen dependence is evident in the electrochemical charge-transfer ability of the Group 5 TMDs whereby tellurides show slower HET rates than sulfides and selenides. We identify VTe2 as the best-performing material for HER contrary to the widely predicted VS2. VTe2 manifests the lowest HER overpotential at 0.5 V vs. RHE and Tafel slope of 55 mV dec(-1). Interestingly, the HER performance of vanadium dichalcogenides and Group 5 tellurides shows chalcogen- and transition metal-dependence, respectively. Reasons behind their HER performance have also been proposed from our theoretical studies found on thermodynamics and kinetics. Broadly, the HER performances of bulk Group 5 TMDs are less outstanding than those expected despite being true metals. This fundamental study provides fresh insights into the electrochemical and electrocatalytic characteristics of metallic Group 5 TMDs that will be indispensable for the development of TMDs in future applications.