Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS₂ Electrodes

Abstract

Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced by a gate electrode lying underneath the MoS2 and separated from it by a dielectric. Application of a voltage to the back-side gate electrode while sweeping the MoS2 electrochemical potential in a conventional manner in 0.5 M H2SO4 results in up to a 140 mV reduction in overpotential for hydrogen evolution at current densities of 50 mA/cm2. Tafel analysis indicates that the exchange current density is correspondingly improved by a factor of four to 0.1 mA/cm2 as gate voltage is increased. Density functional theory calculations support a mechanism in which the higher hydrogen evolution activity is caused by gate-induced increase in the electronic charge on Mo metal centers adjacent to the S vacancies (the active sites), leading to enhanced Mo–H bond strengths. Overall, our findings indicate that the back-gated working electrode architecture is a convenient and versatile platform for investigating the connection between tunable electronic charge at active sites and overpotential for electrocatalytic processes on ultrathin electrode materials.

The Catalytic Mechanics of Dynamic Surfaces: Stimulating Methods for Promoting Catalytic Resonance

“…Performing DFT calculations to assess the change in binding energy of H* on MoS 2 , they found that a -40 to 100 V range in gate voltage correlated to a 16 meV change in the binding energy of H*. (264) Many opportunities exist for dynamic modulation of both binding energies and activation energies of surface reactions using CATFET devices. The main control of the device is through the applied gate voltage, which has ranged from -50 to 100 V in previous experiments.…”

“…(264) This can help overcome limitations of low charge density transfer to the catalyst layer by metal oxides that inherently exhibit low dielectric constants. (264) For the latter, it has been shown through first principles calculations that the polarization can significantly affect the catalytic properties of the thin film catalysts. (288) The extent of these effects depends on the electronic structures of both the metal and the ferroelectrics.…”

Nanoscale Selective Passivation of Electrodes Contacting a 2D Semiconductor

“…This opens a broad spectrum of different combinations of polymers and 2D semiconducting materials. Furthermore, since the HET rate in 2D semiconductors can be nicely regulated by applying different back gate potentials, the FET devices with incorporated back gate could use this advantage to keep the 2D semiconductor in the OFF state during the coating of the electrode contacts. We believe that our demonstration of the method on the devices build on single‐crystal MoS 2 monolayers will be useful for future (bio)sensing devices, especially FET, which are based on 2D TMDCs for label‐free detection and rely on an electronic readout.…”

Promoting Electrocatalytic Hydrogen Evolution Reaction and Oxygen Evolution Reaction by Fields: Effects of Electric Field, Magnetic Field, Strain, and Light

“…Similar improvements have also been demonstrated in another independent work by Wang et al., revealing general availability of such gate‐tuned hydrogen adsorption. [ 70 ]…”

“…[ 71,72 ] For example, the Thomas–Fermi screening length of MoS 2 with an excess electron density of 10 13 cm −2 is only 1−3 nm. [ 70 ] As a result, the intrinsic catalytic activity of surface active sites of multilayer MoS 2 is hardly affected by a gate electric field. [ 57 ]…”