Preparation Of Composite Materials Based On MXene And MoS₂ And Study On Their Hydrogen Evolution And Humidity Sensitivity

Since Geim group first stripped off the monoatomic layer of graphene in 2004,two-dimensional layered materials have quickly attracted great interest of researchers.It has many advantages,such as large specific surface area,high electron mobility,abundant active sites,etc,which make it one of the hot materials in the research of high-performance electronic devices.Among the numerous graphene-like two-dimensional layered materials,transition metal sulfides（TMDs）and transition metal carbon/nitrides（MXene）are the most eye-catching.In this paper,TMD（MoS₂）and MXene（Mo₂CT_x,Ti₃C₂T_x）are the main research objects.Nanomaterials with special morphology were prepared by hydrothermal synthesis,chemical vapor deposition（CVD）and liquid phase stripping,and the nanostructure and morphology growth mechanism were explored by scientific research methods.Based on the different physical and chemical properties of the materials,the application of the materials in humidity sensing and electrocatalytic hydrogen evolution was explored.The main content and research results of this article are as follows:1.Humidity sensing performance of a few layers of dendritic molybdenum disulfidewe report an improved chemical vapor deposition method for the growth of dendritic few-layer MoS₂ nanomaterials.The grown MoS₂ crystals have a dendritic shape with fractal and schedulable patterns.Compared with triangular MoS₂,the fractal dendrite MoS₂ increases the complexity of the structure and exposes more edge active sites,which greatly improves its humidity sensing performance.These morphologies are mainly initiated from the growth of double defects,and can be regulated by the S:Mo vapor ratio by characterizing their atomic structure.This study enhances the understanding of the growth mechanism of twin-derived crystals,extends their application from nanomaterials to two-dimensional crystals,and also provides a powerful and controllable method for the preparation of small-sized transition metal sulfides TMDs.Shape engineering methods in electrochemical applications have evolved.2.Electrocatalytic hydrogen evolution performance of carbon-coated hollow molybdenum disulfide nanosphereswe report the first-principles investigation and synthesis method of the hollow-MoS₂/C heterostructure applied to the hydrogen evolution catalytic material.The first principle was used to calculate the free energy of hydrogen ion adsorption at the heterostructure interface under different surface adsorption ratio.The change of the density of states before and after carbon coating proved that the carbon coating improves the conductivity of the catalyst.Higher reactivity areas and higher conductivity can significantly improve hydrogen evolution catalytic performance,which is also demonstrated by electrochemical testing.Hollow-MoS₂/C exhibits a low onset overpotential of 96 mV and a low Tafel slope of 67.4 mV dec^-1,as well as good catalytic stability.The composite catalyst prepared by the two-step method has a larger specific surface area and a larger porosity,can significantly suppress the collapse and stacking effect caused by the electrode circulation process,and improve the cyclic reversibility and stability of the material.This work is expected to provide a meaningful reference for solving the problem of cycling performance degradation of non-precious metal-catalyzed hydrogen evolution materials.3.2D organ-like molybdenum carbide（MXene）coupled with MoS₂ nanoflowers enhances the catalytic activity in the hydrogen evolution reactionTwo-dimensional MXene materials have a wide range of electrochemical applications.However,the synergistic catalysis of MXene and TMD materials has not been studied in depth.A strategy was proposed to prepare a 2D organ-like Mo₂C MXene matrix derived from Mo₂Ga₂C crystals,coupled with MoS₂ nanoflowers to explore the hydrogen evolution reaction（HER）of molybdenum carbides and disulfides.Compared with Mo₂CT_x（where T_x means F,O,and OH surface terminations）MXene catalysts,MoS₂@Mo₂CT_x nanohybrids showed significantly enhanced HER activity,with a low overpotential of about 176 mV in alkaline media at a current density of 10 mA cm^-22 and a very small overpotential of 26Ω.Density functional theory calculations indicated that the reduction of the hydrogen adsorption energy of the MoS₂@Mo₂CT_x nanohybrids could be attributed to fast electron transport ensured by Mo₂CT_x with intrinsic conductivity and a large number of hydrogen adsorption sites provided by MoS₂ nanoflowers.The synthetic method is promising to tailor the specific properties by preparing organ-like molybdenum carbides coupled with MoS₂ nanoflowers.4.Study on the electrocatalytic hydrogen evolution performance of Ti₃C₂T_x-MXenes intercalated with TiOF₂ nanospheresMXenes is a new type of two-dimensional material with high electrical conductivity and unique surface properties,which has great potential in non-precious metal catalytic hydrogen evolution reactions.However,due to its poor oxidation resistance,it is easy to be oxidized in aqueous solutions,resulting in the loss of its electronic properties and surface activity.In order to improve the stability of MXenes material,we report a simple and effective composite synthesis strategy with TiOF₂intercalation.The TiOF₂@Ti₃C₂Tx prepared by this method shows extremely long catalytic activity life of 1000 cycles in an acidic electrolyte.The catalyst also exhibits high hydrogen evolution reaction activity,with a onset potential as low as 103 mV and a Tafel slope as low as 56.2 mV dec^-1.