Tailoring Polymorphic Heterostructures of MoS₂–WS₂ (1T/1T, 2H/2H) for Efficient Hydrogen\nEvolution Reaction

Abstract

Earth-abundant\nand inexpensive transition metal dichalcogenides\n(TMDCs) with existing polymorphisms (metallic 1T phase and semiconducting\n2H phase) have been proposed as alternatives to noble metals (e.g.,\nPt, Ir, and Ru) to achieve an efficient hydrogen evolution reaction\n(HER). Although the 1T phase of TMDCs (1T-TMDCs) is essential as an\nHER catalyst, practical application in the HER has not been realized\nowing to the lack of any large-scale production of the 1T-TMDC and\n1T/1T-TMDC heterostructure fabrication method. Here, polymorphic TMDC–TMDC\nheterostructures at a 4 in. wafer scale is reported for 1T-MoS₂/1T-WS₂ vertical heterostructures (1T/1T-MWH) or\n2H-MoS₂/2H-WS₂ vertical heterostructures (2H/2H-MWH)\nunder cold plasma conditions and process temperature. Simultaneous\nion-bombardment onto substrates induces a few nanosized grain boundaries\nwith discontinuous films, resulting in exposed edges that act as catalytically\nactive sites. The electrocatalytic performances of the prepared polymorph\n(1T or 2H phases of MoS₂ and WS₂) and polymorphic\nheterostructures of 1T/1T-MWH and 2H/2H-MWH are compared. 1T/1T-MWH\nshows the highest electrocatalytic performance owing to its metallic\n1T phase and heterostructures containing alloy structures at the heterointerface.\nMoreover, the nanosized grains of 1T/1T-MWH preserve their original\nphase after 1000 HER cycles, proving their robustness and durability.