Modulation of Charge Transfer Kinetics By Two Orders of Magnitude at Back-Gated Monolayer MoS2 Electrodes

Charge transfer at the electrode/electrolyte interface is an elementary step in electrochemical reactions and is essential to many electrochemical applications. For a specific reaction, the charge transfer kinetics are largely dependent on the electronic structure at the electrode surface. We demonstrate a continuous and reversible physical method to modulate the charge transfer kinetics at nanometer thick two-dimensional semiconductor electrodes in which a transverse electric field (produced by a gate bias) applied from the back side of the electrode shifts the electrode’s band alignment on the front side. This gate tunable electrode structure is analogous to a metal–oxide–semiconductor field-effect transistor (MOSFET). We find that at back-gated monolayer MoS₂ electrodes, the charge transfer kinetics can be modulated from irreversible to nearly reversible by the back-gate bias. In particular, we were able to tune the charge transfer rate constant for MoS₂ with the ferrocene/ferrocenium redox couple by two orders of magnitude, from 4×10^-6 to 9.7×10^-4 cm/s, with varying back-gate biases. As a general approach, the field effect, with its potential to alter the electrochemical properties of two-dimensional semiconductors over a large range, opens up new possibilities for fundamental studies of gate-tunable electron occupation and Fermi level alignment on electrochemical reactions.