Mechanistic understanding of efficient electrocatalytic hydrogen evolution reaction on a 2D monolayer WSSe Janus transition metal dichalcogenide

Abstract

Ultrathin two-dimensional Janus transition metal dichalcogenides (2D JTMDs) have attracted much attention due to their potential applications in electrocatalysis, sensors, and other electromechanical devices. In the present work, a first principles-based quantum mechanical (QM) hybrid periodic density functional theory (DFT) method has been employed to examine the equilibrium structure, geometry and electronic properties (such as the electronic band structure, band gap and total density of states (DOS)) of a 2D monolayer WSSe JTMD. We have performed non-periodic quantum mechanical DFT computations to find out the most favorable hydrogen evolution reaction (HER) pathway on the W-edges (100) and S-/Se-edges (010) of the 2D Janus WSSe material. The present research shows that the 2D monolayer Janus WSSe TMD follows the Volmer–Heyrovsky reaction mechanism with very low H*-migration and Heyrovsky reaction energy barriers about 2.33–7.52 kcal mol⁻¹ during the H₂ evolution. It was found that the 2D Janus WSSe has a high value of turnover frequency (TOF) of ∼1.91 × 10⁷ s⁻¹ and a very low Tafel slope (m = 29.54 mV dec⁻¹ at T = 298.15 K) due to better overlapping of the d-orbital electron cloud of the W atom and the s-orbital electron cloud of the H₂ appearing in the HOMO–LUMO structure of the Heyrovsky TS. The present study demonstrates the extraordinary HER activity and performance of the 2D monolayer WSSe JTMD. Our research exhibits how to computationally devise a highly active electrocatalyst from 2D JTMDs utilizing their active edges, and the current investigation will boost the further development of superior 2D electrocatalysts for efficient HER.