Edge-site nano-engineering of WS2 by low temperature plasma-enhanced atomic layer deposition for electrocatalytic hydrogen evolution

Edge-enriched transition metal dichalcogenides, such as WS ₂, are promising electrocatalysts for sustainable production of H ₂ through the electrochemical hydrogen evolution reaction (HER). The reliable and controlled growth of such edge-enriched electrocatalysts at low temperatures has, however, remained elusive. In this work, we demonstrate how plasma-enhanced atomic layer deposition (PEALD) can be used as a new approach to nanoengineer and enhance the HER performance of WS ₂ by maximizing the density of reactive edge sites at a low temperature of 300 °C. By altering the plasma gas composition from H ₂S to H ₂ + H ₂S during PEALD, we could precisely control the morphology and composition and, consequently, the edge-site density as well as chemistry in our WS ₂ films. The precise control over edge-site density was verified by evaluating the number of exposed edge sites using electrochemical copper underpotential depositions. Subsequently, we demonstrate the HER performance of the edge-enriched WS ₂ electrocatalyst, and a clear correlation among plasma conditions, edge-site density, and the HER performance is obtained. Additionally, using density functional theory calculations we provide insights and explain how the addition of H ₂ to the H ₂S plasma impacts the PEALD growth behavior and, consequently, the material properties, when compared to only H ₂S plasma.