Impact of Structural Heterogeneities in Hierarchically Grown Microribbons on 2D WS 2 Monolayer on the Measured Local Hydrogen Evolution Activity on Au Substrate

ABSTRACT Homoepitaxial growth of highly crystalline microribbons on large‐area 2D transition metal dichalcogenide (TMD) monolayers is often facilitated by molten salt chemical vapor deposition (CVD) via the vapor–liquid–solid growth method. These microribbons are vertically stacked TMD monolayer stripes that exhibit well‐defined edge structures, introducing spatial heterogeneities across the basal plane of their 2D monolayer supports. Although frequently observed in CVD‐grown TMDs, their influence on local electrocatalytic behavior remains poorly understood. Here, we use scanning electrochemical cell microscopy (SECCM), combined with correlative microscopy and spectroscopy, to spatially resolve the hydrogen evolution reaction (HER) activity of WS 2 monolayer decorated with microribbons at nanometer resolution. Quantitative analysis of over 33 000 localized electrochemical measurements reveals that monolayer edges exhibit twice the catalytic activity of the basal plane, while single‐ and multilayer microribbons suppress HER activity by over 5‐ and 10‐fold, respectively, due to interlayer coupling and sluggish charge transport from the underlying Au substrate. Overall, this work reveals how microribbons modulate basal plane activity in 2D WS 2 on metallic Au substrate and demonstrates how co‐localization of SECCM with various spectroscopies can be used as a powerful technique for mapping nanoscale catalytic activity across structurally complex TMD surfaces.