Defect-rich Crystalline WSe₂ Nanosheets as Efficient Electrocatalysts for Hydrogen Evolution Reaction

The edges of layered transition metal dichalcogenides (TMDs) are recognized as the active sites for electrocatalytic hydrogen evolution, therefore considerable efforts have been devoted to increasing the edge density of TMDs. Given that defect-enriched TMDs are synthesized at mild conditions, their low crystallinity normally results in poor electrochemical stability. Although high-temperature processing is efficient to achieve highly crystalline TMDs, which in turn leads to low electrocatalytic activity due to the loss of reactive defects and edge sites. In this work, defect-enriched WSe₂ with high crystallinity was synthesized via a long-term ultrasonic treatment of crystalline WSe₂ plates in ethanol. Few-layered WSe₂ nanosheets (NSs) were firstly obtained by ultrasonication-assisted exfoliation of WSe₂ plates, while island-like domains were subsequently formed under durable ultrasonication. The resultant defect-rich crystalline WSe₂ NSs possessing large specific surface area, abundant active sites and high crystallinity exhibit superior electrocatalytic performance for hydrogen evolution reaction.