Reversing Interfacial Catalysis of Ambipolar WSe₂ Single Crystal

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.