WS₂ Nanosheets with Highly‐Enhanced Electrochemical Activity by Facile Control of Sulfur Vacancies

Abstract

Abstract Tungsten disulfide (WS 2 ) is a promising and low‐cost material for electrochemical hydrogen evolution reaction (HER) and has been extensively studied due to its excellent performance. However, the development of a facile and controllable defect‐engineering to activate its basal planes is still crucial to improve its HER activity. Here, we put forward an annealing strategy to create controllable sulfur vacancies (S‐vacancies) in ultrathin WS 2 nanosheets, which can result in the increase of active sites and enhanced electrocatalytic activity accordingly. Our density‐functional‐theory (DFT) calculations reveal that the Gibbs free energy of hydrogen adsorption (Δ G H* ) can be tuned to near zero by controlling the density of S‐vacancies, leading to thermal‐neutral HER performance. We find that optimal HER performance can be achieved by tuning the density of S‐vacancies in WS 2 through annealing in the mixture of Ar and H 2 (5 %). The WS 2 nanosheets with the optimal density of S‐vacancies show lower overpotential by 116 mV at 10 mA/cm 2 and smaller Tafel slope by 37.9 mV/dec than as‐prepared counterpart, and super‐excellent stability in acid. Additionally, the WS 2 with optimal S‐vacancies also shows the best HER activity in alkaline solution. Our findings present a facile and general strategy to design electrocatalysts with more active sites, which is applicable to other materials for the improvement of their catalytic activities.