Locally Engineering and Interrogating the Photoelectrochemical Behavior of Defects in Transition Metal Dichalcogenides

Abstract

Transition metal dichalcogenides (TMDs) are attractive materials for a variety of applications in solar energy conversion and electrocatalysis, due to their favorable optical and electrical properties and their unique two-dimensional structures which facilitate the fabrication of wide-area, ultrathin layers. Unfortunately, the basal planes which make up the majority of these materials are relatively inert, and thus a great deal of effort has been directed to engineering favorable, catalytically active defects into these materials. Here, we demonstrate how probe-based electrochemical techniques can be employed as multifunctional tools for locally modifying TMD materials and probing the electrochemical behavior of the resulting defects. Scanning Electrochemical Cell Microscopy (SECCM) was employed to locally anodize exfoliated p-type WSe2 nanosheets, creating hole-like defects within individual basal planes in a highly controllable fashion. Photoelectrochemical SECCM imaging was then employed to characterize the chemical behavior of these engineered defects, revealing significantly enhanced activity toward the Hydrogen Evolution Reaction (HER). Atomic force microscopy studies are presented which suggest these enhancements result from an increased density of monolayer-high step features within the anodized defects. Analysis of the SECCM data in the context of finite element simulations revealed that these enhancements increased with increasing anodization time, with local kinetic rates over 2 orders of magnitude higher than unaltered basal planes.

Electrochemically probing exciton transport in monolayers of two-dimensional semiconductors

“…Recently, our laboratory has been exploring how pipet-based electrochemical techniques, such as scanning electrochemical cell microscopy (SECCM), [26][27][28][29][30][31][32][33][34][35][36][37] can be employed as powerful tools for visualizing carrier transport in 2DSCs. In this approach, carrier generation-tip collection (CG-TC) SECCM, an electrolyte-lled pipet is utilized to detect photogenerated carriers as they drive reactions at a nm-scale electrochemical interface.…”

Directly visualizing carrier transport and recombination at individual defects within 2D semiconductors

“…SECCM has been successfully employed to study the catalytic and photoelectrochemical properties of a variety of materials, including 2DSCs. [56][57][58][59] In the studies presented here, we demonstrate a new "Carrier Generation-Tip Collection" (CG-TC) mode of SECCM designed to quantify carrier diffusion lengths within semiconducting materials and locally probe recombination at individual, well-defined defects. This method is applied to visualize carrier transport within mechanicallyexfoliated n-WSe 2 nanosheets, directly revealing the distance photogenerated holes travel within this material and the dramatic impact individual nanoscale defects can have on transport.…”

Scanning Electrochemical Cell Microscopy Platform with Local Electrochemical Impedance Spectroscopy

“…Therefore, the real resolution of SECCM is equivalent to the contact size between the droplet and the substrate, which is approximately 1–1.5 times the tip diameter. Because of its high spatial resolution, this versatile technology has been applied to detect the local information on electrocatalysis, , electron-transfer kinetics, , photoelectrochemical activity, , electrochemical corrosion, , and so forth.…”