Abstract
An improved understanding of the origin of the electrocatalytic activity is of importance to the rational design of highly efficient electrocatalysts for the hydrogen evolution reaction. Here, an ambipolar single‐crystal tungsten diselenide (WSe2) semiconductor is employed as a model system where the conductance and carrier of WSe2 can be individually tuned by external electric fields. The field‐tuned electrochemical microcell is fabricated based on the single‐crystal WSe2 and the catalytic activity of the WSe2 microcell is measured versus the external electric field. Results show that WSe2 with electrons serving as the dominant carrier yields much higher activity than WSe2 with holes serving as the dominant carrier even both systems exhibit similar conductance. The catalytic activity enhancement can be characterized by the Tafel slope decrease from 138 to 104 mV per decade, while the electron area concentration increases from 0.64 × 1012 to 1.72 × 1012 cm−2. To further understand the underlying mechanism, the Gibbs free energy and charge distribution for adsorbed hydrogen on WSe2 versus the area charge concentration is systematically computed, which is in line with experiments. This comprehensive study not only sheds light on the mechanism underlying the electrocatalysis processes, but also offers a strategy to achieve higher electrocatalytic activity.
Highlights
Fossil fuel, as a dominant energy supply, gives rise to environmental pollution and leads to climate change
There are no PMMA residues and no discontinuities on the WSe2 surface, indicating that the catalytic activity should stem from WSe2 basal plane, rather than from the discontinuities or the defects
It is clearly seen that the WSe2 transistor exhibits the ambipolar transport behavior, where the hole is the dominant carrier for VGS < 0 V and the electron is the dominant carrier for VGS > 0 V.[24]
Summary
As a dominant energy supply, gives rise to environmental pollution and leads to climate change. There are two pathways for generating molecular hydrogen, following either Volmer–Heyrovsky reaction or Volmer–Tafel reaction.[11] the Volmer reaction is the key step in HER and it is strongly dependent on the electron transfer, the density of active sites, and the Gibbs free energy of adsorbed atomic hydrogen.[12,13,14,15] To improve these factors, many strategies have been developed, such as improving the catalyst’s conductance by introducing a conductive network, increasing the number of active sites by making nanostructure, and modifying materials through element doping or compositing.[3,4,7,16,17,18] Among them, the enhancement mechanism through improving conductivity is still unclear, possibly due to the complicated model system with varying factors like active site or nanostructures. The catalytic activity is enhanced, as demonstrated by the decrease of Tafel slope from 138 to 104 mV per decade and the
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