Fabrication of amorphous subnanometric palladium nanostructures on metallic transition metal dichalcogenides for efficient hydrogen evolution reaction

Fabricating solution-processable composite materials of transition metal dichalcogenides (TMDs) with ultrasmall noble metal structures employing an easy preparation method poses a significant challenge. In this study, we utilized a green, one-step synthetic method by directly employing electrochemical lithium intercalation-based exfoliated metallic TMD nanosheets (MoS2, WS2, and TiS2) to reduce palladium ions (Pd2+) to metallic Pd0, leading to the deposition on their surfaces. The resulting Pd nanoparticles (Pd NPs) in composites (Pd-MoS2, Pd-WS2, and Pd-TiS2) were found to be amorphous, with a size ranging from 0.81 to 1.37 nm. The impact of Pd NP size on hydrogen evolution reaction (HER) activity was elucidated. Among the fabricated composites, Pd-MoS2 exhibits the best HER performance, attributed to its smallest Pd NP size (0.81 nm). It shows an overpotential of 70 mV at a current density of 10 mA cm-2, along with a Tafel slope of 43 mV dec-1. These HER performance metrics surpass those of most Pd-decorated 2D catalysts. Metallic transition metal dichalcogenide nanosheets decorated with amorphous subnanometric Pd nanoparticles exhibit comparable HER performance to that of commercial Pt-C.