Nanoscale mapping of electron transfer kinetics and hydrogen evolution on 2D metal-semiconductor van der Waals heterostructures using scanning electrochemical microscopy

Septia Kholimatussadiah^1,2,3,4*, Mohammad Qorbani^3,4, Chih-Yang Huang^3,5,6,7, Raman Sankar⁸, Kuei-Hsien Chen⁷, Li-Chyong Chen^1,3,4

¹Department of Physics, National Taiwan University, Taipei, Taiwan
²Nano Science and Technology, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan
³Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
⁴Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, Taiwan
⁵Molecular Science and Technology, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan
⁶International Graduate Program of Molecular Science and Technology, National Taiwan University, Taipei, Taiwan
⁷Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
⁸Institute of Physics, Academia Sinica, Taipei, Taiwan

* Presenter:Septia Kholimatussadiah, email:s.kholimatussadiah@gmail.com

Electron transfer plays a significant role in many chemical processes, especially in the catalytic reactions involved in electrochemical energy conversion and storage. Revealing the electron transfer behavior at the interface of electrode-electrolyte is thus of great importance. Here we fabricate NbS₂/WSe₂ heterostructures and spatially resolve the nanoelectrochemistry at the interface using Scanning Electrochemical Microscopy (SECM). SECM feedback mapping shows a thickness-dependent electrocatalytic ability of NbS₂, WSe₂, and NbS₂/WSe₂ heterostructures to oxidize the redox species Ru²⁺ back to Ru³⁺. Moreover, SECM generation and collection mode directly map the potential-dependent edge and basal plane activity for the hydrogen production. As expected from its metallic nature compared with semiconducting WSe₂, NbS₂ shows almost ten times higher electron transfer rate and lower overpotential to produce hydrogen. On the other hand, few-layer WSe₂ shows better stability in electrochemical environment, faster electron transfer, and higher hydrogen production compared with monolayer and bilayer. Furthermore, finite element method based numerical simulations using MATLAB^® and COMSOL Multiphysics^® is performed to calculate the reaction rate constants k₀ and simulate the steady-state concentration gradient. Finally, the nanoelectrochemistry at the NbS₂/WSe₂-electrolyte interfaces are spatially resolved which has never been reported before and understanding this behavior will be useful for future electrochemical devices.

Keywords: scanning electrochemical microscopy, two-dimensional materials, metal-semiconductor heterostructures, electron transfer, hydrogen evolution reaction