Constructing Mono-/Di-/Tri-Types of Active Sites in MoS₂ Film toward Understanding Their Electrocatalytic Activity for the Hydrogen Evolution

The availability and catalytic activity of the cost-efficient electrocatalysts are the dominant factors for the hydrogen evolution reaction (HER) performance in the renewable hydrogen economy. Extensive efforts have been devoted to maximize the amount of various active sites in non-noble-metal electrocatalysts for HER. This work reported a physically sputtering strategy to construct porous and ordered 2H-MoS2 films with mono-/di-/tri-types of active sites via controlling the film thickness (from ∼15 to 3050 nm) in the energetic plasma. As the pure (2H-) MoS2 for HER electrocatalyst, the as-fabricated 3050 nm additive-free columnar film electrode shows a stable electrochemical activity for HER (an overpotential of 204 mV at a current density of −10 mA/cm2). Interestingly, the MoS2 film with controllable thickness can serve as an innovative platform to study the electrocatalytic activity of the customized different active sites (the exposed active edge of sheets (eE), stepped-termination surfaces (sS), and terrace on the basal planes (tB)) and the dependence of electrocatalytic efficiency of the vertically aligned MoS2 eE active sites on their distance to the current collector. The results first revealed that the tB active sites possessed almost the same electrocatalytic activity as that of the eE active sites but higher than the sS active sites. The electrocatalytic efficiency of the eE active sites decreased as their distances to the current collector were gradually increasing, due to the limited conductivity of the semiconductive 2H-MoS2 sheets. This work proposes and evaluates a facile strategy for replying to the question of how to investigate the electrocatalytic activities of various active sites in the electrocatalysts.