Temperature-Controlled Cold Plasma Synthesis of MoS₂−WS₂ (1T/1T, 2H/2H) Polymorphic Heterostructures for Hydrogen Evolution Reaction

Transition metal dichalcogenides (TMDs) are attracting considerable interest due to their outstanding electrical and chemical properties, high carrier mobility, low power consumption, and exceptional flexibility and stretchability. Beyond these advantages, TMDs show great promise as catalysts for the hydrogen evolution reaction (HER). However, the practical application of two-dimensional (2D) materials has been hampered by inadequate phase control methods for TMDs. Current techniques, including post-treatment chemical processes, lattice deformation via ion collision, and strain-induced phase control, involve additional steps and yield low efficiency, limiting their practicality.<br/><br/>This research explores the design and characterization of polymorphic heterostructures of MoS₂ and WS₂, utilizing a novel temperature-regulated cold plasma-enhanced chemical vapor deposition (PECVD) method. By varying the substrate temperature while keeping plasma parameters constant (power, pressure, processing time, and gas ratio), this approach significantly enhances the versatility of TMDs.<br/><br/>The method facilitates the production of 1T-MoS₂/1T-WS₂ (1T/1T-MWH) and 2H-MoS₂/2H-WS₂ (2H/2H-MWH) vertical heterostructures on a large 4-inch wafer scale. Cold plasma conditions, combined with ion bombardment, result in the formation of nanoscale grain boundaries and exposed edges that significantly boost catalytic activity. Techniques such as high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) confirm the successful creation and stability of these polymorphic forms.<br/><br/>Electrochemical tests indicate that the 1T/1T-MWH displays superior HER performance, featuring a lower overpotential and enhanced stability compared to other polymorphic variants. This improved performance is attributed to the metallic properties of the 1T phase, which enable rapid charge transfer, and the alloy structures at the heterointerface, which lower reaction energy barriers.<br/><br/>Further analysis after HER cycles shows that 1T/1T-MWH retains its phase stability and catalytic efficiency even after 1000 cycles, proving its durability. This innovative synthesis approach offers a scalable and effective method for creating high-performance HER catalysts, underscoring the potential applications of TMD polymorphic heterostructures in renewable energy solutions.<br/><br/>Acknowledgement: This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education 2022R1A6A3A13063381 and 2022R1A3B1078163). And this work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No.2022R1A4A1031182).