Catalytic properties of group 4 transition metal dichalcogenides (MX2; M = Ti, Zr, Hf; X = S, Se, Te)
Interest in layered transition metal dichalcogenides (TMDs) has proliferated due to their properties, making them promising materials for electrochemical applications. Despite this, almost exclusive attention has been placed on group 6 TMDs. Hitherto, there has been a lack of understanding of the electrochemical behaviour of group 4 TMDs, which could serve as promising materials for electrochemical applications with their semiconducting properties. In this work, we provide a first insight into the inherent electrochemistry of group 4 TMDs (i.e., TiS2, TiSe2, TiTe2, ZrS2, ZrSe2, ZrTe2, HfS2, HfSe2 and HfTe2) and their catalytic activities towards the hydrogen evolution reaction (HER). In particular, HfS2 is electrochemically inert within a wide potential range of -1.8 V to +1.8 V vs. Ag/AgCl and displays superior HER activity compared to the other group 4 TMDs, making it a promising candidate for electrochemical sensing applications. Towards the aim of tuning their HER catalytic properties, the materials are subjected to electrochemical treatment. Electrochemical activation towards the HER is displayed for ZrSe2 and HfSe2 via both electrochemical oxidation and reduction, and TiTe2 via electrochemical reduction. X-ray photoelectron spectroscopy (XPS) analysis points towards the importance of material purity in tuning the catalytic performances of group 4 TMDs. Such findings provide a foundational understanding of the electrochemistry of group 4 TMDs, which when applied appropriately can springboard this field of research towards achieving aims in electrochemical applications.