Stabilizing Sulfur Vacancy Defect by A “Click” Chemistry of Ultrafine Palladium to Trigger High-Efficiency Hydrogen Evolution of MoS2

Defect engineering is widely applied in transition metal dichalcogenides to produce high-purity hydrogen. However, the instability of vacancy states on catalysis still remains a bigger challenge. Here, our first-principles calculations discover that, by optimizing the asymmetric S vacancy in the highly asymmetric 1T′crystal of layered bitransition metal dichalcogenides (Co-MoS2) in light of Pd modulation, the metastable phase and the amount of active sites in the structure can be reduced and increased, respectively, leading to the further boosted HER activity toward layered bi-transition metal dichalcogenides. Thus, we report a “Click” chemistry strategy to make such a catalyst with engineered unsaturated sulfur edges by a strongly coupling effect between ultrafine Pd-ensembles and Co-MoS2 nanosheets. As expected, the Pd-modulated Co-MoS2 nanosheets exhibit a very low overpotential of 60 mV at 10 mA cm-2 with a small Tafel slope (56 mV dec-1) for HER in 1.0 M PBS, comparable to commercial Pt/C. In addition, its high HER activity can be still retained in acidic and alkaline conditions. Both the theoretical and experimental results reveal that Pd-ensembles can efficiently activate and stabilize the inert basal plane S sites during HER processes by the formation of Pd-S in Co-MoS2. This work not only gains a deeper understanding of the correlation between defect sites and intrinsic HER catalytic properties for transition metal chalcogenide (TMDs)-based catalysts, but also offers new insights into better designing earth-abundant HER catalysts with high efficiency and durability.