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<p>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 4 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 electronic charge on Mo metal centers adjacent 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.</p></div></div></div><br><p></p></div></div></div>