(668f) Continuous, Efficient Control of Electrochemical Phenomena on Back-Gated 2D Electrodes

Understanding and controlling interfacial electrochemical phenomena (e.g. electric double layer charging, heterogeneous charge transfer and surface binding of reaction species on the electrode) is key to optimizing energy conversion and storage systems including batteries, fuel cells, and supercapacitors. In recent publications,^1,2 we reported a back-gated electrode structure that enables real-time, continuous and efficient control of heterogeneous charge transfer kinetics. Such back-gated electrodes were fabricated with nanometer-thick semiconductors (i.e. 5 nm ZnO and monolayer MoS₂) on SiO₂/degenerate Si back gates, analogous to metal–oxide–semiconductor field-effect transistors (MOSFETs). Our previous results showed that the heterogeneous charge transfer rate constant for 2D semiconductors can be tuned by up to 200 times, due to the gate-induced charge carriers and band alignment shift at the electrode/electrolyte interface. In this presentation, we introduce an improved device structure utilizing microfluidics, which allows steady-state analysis of heterogeneous charge transfer kinetics, as well as examinations of electrocatalytic reactions where surface binding energies often determine reaction rates. Using such devices, we are able to modulate the charge transfer rate constant between graphene and ferrocene by one order of magnitude with varying back-gate biases and reduce the catalytic overpotential of hydrogen evolution reaction on monolayer MoS₂ by manipulating the electron occupation with field-effect charging. These results further demonstrate how the electronic structure at the electrode/electrolyte interface affects the electrochemical behaviors. Overall, the approach introduced here is generally applicable to modulating and analyzing interfacial electrochemical phenomena in various electrochemical systems and offers new insights for optimizing electrochemical properties of 2D materials.

(1) Kim, C.-H.; Frisbie, C. D. Field Effect Modulation of Outer-Sphere Electrochemistry at Back-Gated, Ultrathin ZnO Electrodes. J. Am. Chem. Soc. 2016, 138 (23), 7220–7223.

(2) Wang, Y.; Kim, C.-H.; Yoo, Y.; Johns, J. E.; Frisbie, C. D. Field Effect Modulation of Heterogeneous Charge Transfer Kinetics at Back-Gated Two-Dimensional MoS₂ Electrodes. Nano Lett. 2017, 17 (12), 7586–7592.