Fabrication,Modification And Catalytic Application Of Transition Metal Sulfur/Nitrogen Group Compounds

As a clean,sustainable and high energy-dense power source,hydrogen is one of the best approaches to solve the current energy crisis.Based on solar,wind and water energy,it is convenient to transform their discontinuous electric output to hydrogen for storage,transportation and use.Water splitting by electrolysis is the key link for the transformation above,which needs catalysts to reduce the consumption of electric energy.The current catalysts usually rely on the noble metals that are expensive and scarce.Hence,it is urgent to exploit high-performance and non-noble metal based catalysts to replace noble metals.Transition metal compounds（TMCs）that are abundant and cheap have been treated as the promising alternative to replace the current noble metals.However,the catalytic performance of TMCs is weaker than noble metals.Therefore,it is meaningful to modify TMCs to improve their electrocatalytic performance.The target of this work is the modification of TMCs from the perspectives of hetero-structure,morphology and defect.Moreover,ion implantation has also been adopted to modify the interface of conventional electrodes and improve the catalytic performance.The contents consist of the following points:（1）WS₂-CoS₂hetero-structure supported on the hydrophilic carbon paper has been synthesized by hydrothermal and chemical vapor deposition（CVD）methods.Owing to the synergistic effect,the synthesized WS₂-CoS₂hetero-structure exhibits excellent hydrogen evolution reaction（HER）catalytic activity.In 0.5 M H₂SO₄,the overpotential at 100 m A·cm^-2 is 245 m V,and the Tafel slope is 270 m V·dec^-1.Through the characterizations of morphology,crystal phase,chemical state and specific surface area,it can be found that the WS₂-CoS₂hetero-structure has a uniform distribution.WS₂nanosheets effectively limit the aggregation of CoS₂nanoparticles to increase the specific surface area.CoS₂nanoparticles can fill the intervals of WS₂nanosheets to promote the transfer of electrons.Moreover,the crystal lattice distortion on the interfaces between two phases may make the electronic structure change and then improve the catalytic performance.This work supports the guidance for the design of other hetero-structures.（2）Zn-incorporated mesoporous cobalt phosphide nanowire arrays supported on Ni foam have been synthesized by hydrothermal and CVD methods.Owing to the unique morphology and crystal phase induced by Zn incorporation,this sample exhibits excellent catalytic performance.In 0.5 M H₂SO₄ and 1.0 M KOH,the overpotentials at 100 m A·cm^-2 are 167 and 172m V,respectively.Through the characterizations of morphology,crystal phase and specific surface area,Zn incorporation has affected the morphology of cobalt phosphide nanowires and induced large amounts of mesopores to appear on the surface.In addition,Zn incorporation can also increase the proportion of CoP phase,which can improve the catalytic activity dramatically.This work can support new direction for the morphology modification.（3）Electron irradiation has been adopted to modify tungthen chalcogenides.Through Raman characterization,HER and H₂O₂decomposition electrocatalytic investigation,it has been found that electron irradiation can strip the two-dimentional layered WS₂ from bulk to monolayer.Moreover,electron irradiation can also break the chemical bonds on the surface and induce the materials to be oxidized during irradiation.These two points may affect the catalytic performance.Each material has its own optimal irradiation dose.If the irradiation dose is larger than this limited value,the broken bonds will increase and aggravate the surface amorphization,which may negatively affect the total catalytic performance.The bond strength is the key that affects the irradiation effect.This work supports a guidance for the modification by electron irradiation.（4）Ion implantation has been used to modify Cu and carbon fiber electrodes.Through electrochemical impedance spectrum（EIS）,surface resistance and enzyme-like catalysis characterizations,it can be found that ion implantation can affect the interfacial charge transfer efficiency and catalytic activity,which is related to the combination of ion species and substrates.The interfacial impedance of Cu substrate does not decrease,due to its high chemical activity and oxidability.The catalytic activity of carbon fiber electrode has been influenced obviously for the accessibility of metal nanoparticles to the electrolyte,due to its loose structure and catalytic sluggishness.This work supports reference for the application of ion implantation on the modification of materials.