Facile fabrication of conductive MoS2 thin films by sonication in hot water and evaluation of their electrocatalytic performance in the hydrogen evolution reaction

Molybdenum disulfide (MoS2) has long been used in catalysis and is a promising material for energy conversion devices. In order to utilize MoS2 in electrocatalytic applications, it needs to be sufficiently conductive. Even though a metallic 1T phase of MoS2 exists, its exfoliation process is expensive and difficult to scale because it involves hazardous materials and procedures, limiting its practical applications. We have previously reported an efficient and environmentally friendly procedure to exfoliate conductive MoS2 via sonication in very dilute aqueous hydrogen peroxide. Here, we report a new way of exfoliating heavily doped conductive MoS2 by sonication in pure water at 60 °C without additives. Conductivity measurements, Raman spectroscopy and X-ray photoelectron spectroscopy demonstrate that controlling the sonication time and temperature lead to the generation of small quantities of hydrogen peroxide in the water that interact with MoS2 to form a small amount of sub-stoichiometric MoO3-y. This impurity acts as a dopant and is responsible for the increase in conductivity of the MoS2 films without compromising their structural integrity. We also evaluate the performance of the doped MoS2 films as electrocatalysts in the hydrogen evolution reaction. We elucidate the mechanistic origin of the catalytic properties of these materials which may be of future use to develop a family of electrocatalysts based on doped MoS2.