CoSe₂/MoSe₂ Heterostructures with Enriched Water Adsorption/Dissociation Sites towards Enhanced Alkaline Hydrogen Evolution Reaction

Transition-metal dichalcogenides (TMDs) are promising electrocatalysts toward the hydrogen evolution reaction (HER) in acid media, but they show significantly inferior activity in alkaline media due to the extremely sluggish water dissociation kinetics. Herein, CoSe₂/MoSe₂ heterostructures with CoSe₂ quantum dots anchored on MoSe₂ nanosheets are synthesized towards enhanced alkaline HER catalytic activity. The incorporation of CoSe₂ is intended to construct additional water adsorption sites on the basal planes of MoSe₂ to promote water dissociation. The CoSe₂/MoSe₂ heterostructures show substantially enhanced activity over MoSe₂ and CoSe₂ in 1 m KOH. The optimal overpotential required to reach a current density of 10 mA cm⁻² is merely 218 mV, which is more than 100 mV greater than that of MoSe₂, which is by far the best performance demonstrated for precious-metal-free catalysts. Detailed analyses based on electrochemical testing demonstrate that the water adsorption and subsequent dissociation process is accelerated by CoSe₂ species with rich edge sites; meanwhile, MoSe₂ species provide sufficient active sites for the adsorption and combination of adsorbed hydrogen (H^.). These results provide an effective strategy for developing earth-abundant catalysts with high activity for the alkaline HER, and are of great significance to promote the practical application of alkaline water electrolysis.