Electrochemical imaging uncovers the heterogeneity of HER activity by sulfur vacancies in molybdenum disulfide monolayer

Abstract

Engineering of sulfur vacancies on the basal plane of molybdenum disulfide (MoS₂) may provide effective way to promote the catalytic activity. Although the sulfur vacancy density has previously been correlated with catalytic activity, direct evidence that vacancies create surfaces with enhanced electrocatalytic activity is still lacking. Here, we used a combination of scanning electrochemical cell microscopy (SECCM) with submicrometer resolution and photoluminescence imaging to show that sulfur vacancies in monolayer MoS₂ microflakes lead to significant spatial heterogeneity in the electrochemical hydrogen evolution reaction (HER) activity. Specifically, colocated multi-microscopy unveils that regions with superior HER activity are associated with sulfur vacancy defects. As the vacancy density increases, the triangular flakes display significantly enhanced and spatially uniformly distributed electrocatalytic activity. Our multi-microscopic imaging approach using SECCM convincingly highlights the spatial heterogeneity of electrocatalytic activity across monolayer MoS₂ by sulfur vacancy engineering.