High phase-purity 1T′-MoS2- and 1T′-MoSe2-layered crystals

Phase control plays an important role in the precise synthesis of inorganic materials, as the phase structure has a profound influence on properties such as conductivity and chemical stability. Phase-controlled preparation has been challenging for the metallic-phase group-VI transition metal dichalcogenides (the transition metals are Mo and W, and the chalcogens are S, Se and Te), which show better performance in electrocatalysis than their semiconducting counterparts. Here, we report the large-scale preparation of micrometre-sized metallic-phase 1T ′ -MoX 2 (X = S, Se)-layered bulk crystals in high purity. We reveal that 1T′-MoS 2 crystals feature a distorted octahedral coordination structure and are convertible to 2H-MoS 2 following thermal annealing or laser irradiation. Electrochemical measurements show that the basal plane of 1T′-MoS 2 is much more active than that of 2H-MoS 2 for the electrocatalytic hydrogen evolution reaction in an acidic medium. The phase in which a crystal exists can have a direct influence over its properties; however, it is usually difficult to control during synthesis. Now it has been shown that micrometre-sized metallic 1T′-MoS 2 - and 1T′-MoSe 2 -layered crystals can be prepared in high phase purity on a large scale, and that they display promising electrocatalytic activity towards the hydrogen evolution reaction.