Session:

Tailoring electron transfer dynamics across solid-liquid interfaces are fundamental to electrical and chemical energy interconversion. Marcus–Gerischer¹ formalism suggests that the electronic states of the electrode around the Fermi level have a significant influence on the rate of electron transfer. Studies have also shown that the faster electron transfer kinetics observed on introducing defects is due to localized enhancements in the electronic states around the fermi level that are available to participate in the reaction. Electrostatic gating in field effect transistor mode is one of the widely used strategies to manipulate the charge carrier density and energy band alignment in semiconductors. It has been demonstrated that the heterogeneous charge transfer kinetics at the MoS₂ monolayer² is strongly modulated by applying an external electric field on the working electrodes. Herein, I reevaluate the electric field effect on the interfacial electron transfer at a few layers MoS₂ using Scanning Electrochemical Cell Microscopy (SECCM). MoS₂ electrodes were fabricated in a field effect transistor (FET) configuration with a solid-state graphite bottom gate. The bottom gate voltage (V_BG ) applied to graphite was used to alter carrier density and control the band alignment. I combined in-situ SECCM experiments with the electrostatic manipulation of the band alignment with V_BG to study the effect of charge carrier concentration on the interfacial electron transfer. I also obtained spatially resolved voltammetric responses to understand the role of in-plane charge transport in governing the electrochemical responses of 2D electrodes, especially at conditions of low carrier densities. The experimental approach and results presented here serve as a benchmark for future studies of the electrochemical behavior of two-dimensional materials.

References:
1. Gerischer, H. Electron-transfer kinetics of redox reactions at the semiconductor/electrolyte contact. A
new approach. J. Phys. Chem., 95, 3, 1356–1359 (1991).
2. Wang, Y., et al. Field Effect Modulation of Heterogeneous Charge Transfer Kinetics at Back-Gated
Two-Dimensional MoS 2 Electrodes. Nano Lett. 17, 7586-7592 (2017).

Co-Author(s): Kwabena Bediako (University of California Berkeley)

Sonal Maroo

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