Nanoscale Photoelectrochemical Mapping of Two-Dimensional Electrodes

Abstract

Electron transfer plays a significant role in many chemical processes, especially in the catalytic reactions involved in photoelectrochemical energy conversion and storage. Revealing the electron transfer behavior at the interface of electrode-electrolyte is thus of great importance. Here we fabricate atomically thin semiconductor MX2 (M = Mo, W; X = S, Se) by chemical vapor deposition method and directly map the photoelectrochemical behavior using Atomic Force Microscopy-combined with light-induced Scanning Electrochemical Microscopy (AFM-SECM). AFM-SECM feedback mapping shows a layer-dependent photoelectrocatalytic ability of MX2 to oxidize the redox species Ru2+ back to Ru3+. Moreover, AFM-SECM generation and collection mode shows the potential-dependent edge and basal plane activity for the hydrogen evolution reaction of WSe2. Compared with monolayer and bilayer, few-layer WSe2 shows better stability in an electrochemical environment, faster electron transfer, and higher hydrogen production. Furthermore, finite element method based numerical simulations using MATLAB® and COMSOL Multiphysics® is performed to calculate the electron transfer rate constants k0 and simulate the steady-state concentration gradient. Finally, the photoelectrochemistry at MX2 electrode-electrolyte interfaces are spatially resolved and understanding this behavior will be useful for the future photoelectrochemical devices.