Synthesis Of Vanadium Tetrasulfide Nanostructures For Efficient Electrocatalytic Hydrogen Evolution

Transition-metal chalcogenides have been regarded as promising hydrogen evolution reaction(HER)electrocatalysts with advantages of unique electronic structures,high electrocatalytic activities,and outstanding chemical stability.Vanadium disulfide(VS₂)with a layered structure is an outstanding electrocatalyst with excellent hydrogen adsorption Gibbs free energy,high conductivity and excellent thermal stability in acid solution.Vanadium tetrasulfide(VS₄)as another vanadium containing compound,has a one-dimensional chain-like crystal structure with a large chain spacing(0.583 nm),a high sulfur content and a band gap of approximate 0.8 e V.VS₄ nanostructures have been widely employed in metal-ion storage devices,including Na/Li-ion batteries and Li-S batteries,etc.However,the application of VS₄ as an electrocatalyst in water electrolysis has been scarely reported.The main reason may be that semiconducting VS₄ has low electronic conductivity and low catalytic activity.In this thesis,we designed and fabricated VS₄ nanostructures as advanced HER catalysts by means of introducing sulfur vacancy,oxygen doping,and hybridizing conductive rGO nanosheets.The main research results are as follows:(1)The VS₄ microspheres featuring oxygen doping and abundant sulfur vacancies are synthesized by a simple solution method.The O-doping and S-vacancy offer the VS₄with a dramatically narrowed bandgap and an improved intrinsic electronic conductivity,benefitting for fast charge transport during HER process.On the other hand,the rich defects of sulfur vacancies and oxygen heteroatoms provide more active sites with high activity for catalyzing protons to hydrogen reaction.Owing to the synergistic effects of defect engineering and electronic benefits,the VS₄ microspheres serve as a superior HER catalyst surpassing the 1T-VS₂ microflowers with a layered structure.The VS₄ microsphere catalyst exhibits prominent kinetic metrics of a low onset potential of 15mV,a low overpotential of 48 mV at 10 m A cm^-2,a small Tafel slope of 44 mV dec^-1and a stable long-term operation of 75 h.(2)The VS₄/rGO composite is prepared by grow VS₄ nanorods on surface of GO nanosheets.The content of VS₄ nanorods is tunable.Conductive rGO nanosheets can not only suppress aggregation of VS₄ nanorods,but also serves as conductive matrix to improve the electronic conductivity of catalyst and facilitate fast charge transfer in HER process.Compared with the pristine VS₄ nanospheres,the VS₄/rGO composite has a larger electrochemical active surface area,indicating increased number of active sites.An optimized VS₄/rGO(2:1)catalyst has the smallest Tafel slope of 42 mV dec^-1,the lowest overpotential(?₁₀)of 37 mV and excellent stability(70 h).