Controlled Synthesis And Properties Of Doped Transition Metal Selenide Based Electrocatalysts

The exhaustion of fossil fuels leads us to search for a new type of energy to replace it,among which hydrogen energy has the advantages of high energy density,safety and no pollution,so it becomes the focus of new energy.Among the many ways to prepare hydrogen energy,electrolysis of water has gained wide attention for its simple operation and high efficiency.Although precious metal based catalysts have excellent electrocatalytic performance,their development is limited by their limited reserves.Therefore,the preparation of a high efficiency,low cost electrocatalyst has been the focus of researchers.Among the transition metal compounds,selenides have certain potential in electrocatalytic hydrogen evolution due to their unique 2-dimensional structure,but the properties of selenides need to be improved.In this paper,by doping atoms,constructing morphology and heterojunction,more active sites were exposed and the activity of active sites was increased,so as to improve the electrocatalytic properties of materials.In this paper,Ni Mo Se O,Mo Ni Se S,Ni Co Se@Ni（OH）₂ was prepared by solvothermal method,hydrothermal method,calcination method and other simple synthesis processes,and its electrocatalytic performance was studied.The main research results are as follows:（1）The introduction of heteroatom can improve the activity of the active site in the electrocatalyst.Firstly,Ni Mo O₄ nanorods were synthesized by hydrothermal method and low temperature calcination method,and then Se was doped by partial selenization method.On the one hand,this nanorod structure can expose more active sites with the help of the 3D skeleton structure of nickel foam,and on the other hand,it is beneficial to electron transport and gas escape.Moreover,the doping Se can increase the activity of the active site.In the process of experiment,the addition of selenium powder in selenifying process was also explored.When the amount of selenium powder was 0.25g,the catalyst showed the best properties.（2）As a result of selenide morphology more difficult to control,therefore in the process of synthesis,Mo S₂ nanoneets synthesized on nickel foam firstly coated on the parcel Ni₃S₂ nanorods composite structure,and then through the selenide,on the surface in situ generated selenide,avoiding the accumulation of selenide,and maximum exposed active site,and Se doping can also weaken the S-H.During the experiment,the effect of Mo addition on the properties of the product was also investigated.Through physical characterization,it can be seen that too much or too little Mo can not form the structure of the nanorods wrapped by the nanosheets,thus affecting the electrocatalytic properties.The Mo source was replaced by W source during the experimental system,and the catalytic activity of the product was also improved to the influence after doping Se.（3）The structure of heterojunction has the influence on the improvement of electrocatalyst properties.Therefore,in the first step of synthesis process,the composite of sulfide and nickel hydroxide is formed firstly,and then the composite of selenide and nickel hydroxide is obtained through the second step of selenization reaction.The experimental results show that the amount of Co will affect the thickness of the nanosheet,and too thin or too thick of the nanosheet is not conducive to the exposure of active sites,thus affecting the properties of the electrocatalyst.Moreover,the heterojunction formed by nickel selenide and nickel hydroxide can accelerate the electron transfer and improve the catalytic activity of the products.Nickel hydroxide also speeds up the decomposition of water,speeding up the reaction process.In summary,when the amount of Co is 2 mmol,the material has the optimal properties.