Rational design of freestanding MoS2 monolayers for hydrogen evolution reaction

Molybdenum disulfide (MoS2) presents a promising nonprecious catalyst for hydrogen evolution reaction (HER) that has attracted extensive interest, but it still lacks an effective way to advance the utilization, in particular the basal plane of freestanding 2H-MoS2 for HER. Herein, we report a rational design of freestanding 2H-MoS2 monolayers to maximize the synergistic activity for HER by combining crystallinity engineering and cobalt substitution. Electrochemical measurements and density functional theory calculations indicate that the combination of crystallinity engineering and cobalt substitution in monolayer 2H-MoS2 can not only introduce massive defects that act as new active sites but also activate and make use of the basal plane, which is responsible for the much enhanced HER activity compared to independent crystallinity engineering or cobalt substitution. Impressively, when integrated with a photoharvester cadmium sulfide for photocatalytic hydrogen evolution, the synergistic effect also promotes an excellent cocatalytic performance of monolayer 2H-MoS2 that even higher than platinum (Pt). This study potentially provide new avenues for designing more efficient MoS2-based and other layered materials with enhanced HER performance.