Controllable Syntheses And Electrocatalytic Applications Of Metallic Transition Metal Dichalcogenides

Two-dimensional(2D)metallic transition metal dichalcogenides(MTMDCs)have received great research attention due to their exotic physical properties(such as charge-density wave(CDW)order and superconductivity)and potential applications in nano-electronics and energy-related fields.MTMDCs nanosheets can be used to create unique electronic devices,such as oscillators and memristive phase switching devices.Furthermore,MTMDCs exhibit superior electrocatalytic performances for the hydrogen evolution reaction(HER),which are promising to replace the Pt-based catalysts.To fully promote the fundamental researches or the versatile applications of such 2D MTMDCs,the preparation of ultrathin nanosheets with high crystalline quality is highly needed.The aim of this thesis focuses on the controllable syntheses of the high-quality MTMDCs nanosheets through chemical vapor deposition(CVD)method,and their applications in electrocatalytic HER.This dissertation contains the following four parts:1.The syntheses of high-quality 2D TaS2 nanosheet powders were achieved by using the cost-effective,easily scalable,micro-crystalline NaCl crystals as templates,through a facile atmospheric pressure CVD(APCVD)process.This synthetic route is perfectly compatible with a green transfer process through a facile water dissolution-filtration process to obtain high-purity TaS2 nanosheet powders by virtue of the high solubility of NaCl in water.To explore the growth mechanism,the nucleation and growth behaviors of 1T-TaS2 on NaCl crystals were also examined and explained by performing density functional theory(DFT)calculations.The high-quality 1T-TaS2 nanosheet powders are employed as high-efficiency electrocatalysts in hydrogen evolution reaction.2.Through further parameter optimization,the NaCl template method was extended to the preparation of other MTMDCs nanosheet powders.Then the production of high-quality NbS2 and V5S8 nanoflake powders was achieved.Meanwhile,the crystal structures and basic physical properties of these two materials were characterized.The NaCl-template growth method is testified as a universal and effective strategy for batch preparation of MTMDCs materials.3.The synthesis of vertical 1T-TaS2 on nanoporous gold(NPG)substrates was achieved though a facile chemical vapor deposition route.The effects of various growth parameters on the growth direction,thickness and domain size of TaS2 nanosheets were discussed in detail.Thus,the growth mechanism of vertical TaS2 nanosheets on porous gold was elucidated.The TaS2 nanosheets were proved as high-quality 1T phase single crystal by various characterization methods.This work provides a new idea for the controllable preparation of MTMDCs nanosheets with three-dimensional structure.4.The applications of the vertically oriented 1T-TaS2 nanosheets on NPG were explored as high-efficiency electrocatalysts in hydrogen evolution reaction.Through a series of electrocatalytic comparison experiments,the advantages of the vertical structure in the electrocatalytic process were revealed.The influence of the phase states of 1T-and 2H-on the catalytic activity of as-grown TaS2-was also explored according to both experimental analyses and theoretical calculations.This work provides an important basis for further research on the electrocatalytic performance and practical application of TaS2.