Study On The Electrocatalytic Activity Of Two-dimensional Molybdenum Disulfide Nanomaterial Towards The Hydrogen Evolution Reaction

Hydrogen has been considered as the clean and renewable energy source of the next generation by virtue of its high energy density and environmentally friendly combustion product.Electrochemically evolving hydrogen by splitting water is one of the most efficient and sustainable strategies for hydrogen generation.Up to date,hydrogen evolution can be easily achieved by electrolysis using precious metals,such as Pt,Pd,and Rh.The scarcity and high cost of these precious metals have seriously hampered their practical utilization.Previous studies have revealed that two-dimensional layered molybdenum disulfide(MoS2)based materials would be the promising HER catalysts.However,pristine MoS2 has poor electron transport property and requires very large overpotential to achieve considerable turnover frequencies of HER.Decreasing the overpotential of HER on MoS2 based materials remains a significant challenge.To address this issue,tremendous strategies have been proposed to improve the catalytic activity of MoS2 toward HER:increasing the number of active sites,enhancing the intrinsic activity,and promoting the electron transport rate.The present Master Degree Thesis focuses on these two issues and following work was performed.1.Enhanced hydrogen evolution catalysis from chemically exfoliated metallic MoS2 nanosheetsPromising catalytic activity from molybdenum disulfide(MoS2)in the hydrogen evolution reaction(HER)is attributed to active sites located along the edges of its two-dimensional layered crystal structure,but its performance is currently limited by the density and reactivity of active sites,poor electrical transport,and inefficient electrical contact to the catalyst.Here we report that dramatically enhanced HER catalysis with lower overpotential of-260 mV vs.RHE and lower Tafel slope of 91 mV/decade can be achieved from metallic nanosheets of 1T-MoS2 chemically exfoliated via lithium intercalation from semiconducting 2H-MoS2 nanostrures.Systematical characterizations and electrochemical studies confirm the importance of low-loss electrical transport and proliferated density of catalytic active sites in determining the HER kinetics on the metallic MoS2 polymorph material.These distinct features of IT-MoS2 make the metallic nanosheets as a highly competitive earth-abundant HER catalyst.2.Enhanced electrocatalytic properties of transition-metal dichalcogenides sheets by spontaneous gold nanoparticle decorationWe report that transition-metal dichalcogenides MoS2 can be decorated with gold nanoparticles by a spontaneous redox reaction with hexachloroauric acid aquesous solution.The resulting gold nanoparticles tend to grow at defective sites,and therefore,selective decorations at the edges and the line defects in the basal planes of bulk single crystals were observed.The lithium intercalation-exfoliation process makes the basal planes of chemically exfoliated MoS2 sheets much more defective than their single-crystalline counterparts,leading to a more uniform and higher-density deposition of gold nanoparticles.Due to the greatly improved charge transport between adjacent sheets,the resulting Au-MoS2 hybrids show significantly enhanced electrocatalytic performance toward hydrogen evolution reactions.