Preparation Of Ni-based Electrocatalysts And Their Study In Electrocatalytic Hydrogen Evolution Reaction

With the increase of energy demand in human society and the energy crisis,global warming and environmental pollution caused by the increasing use of fossil fuels,it is of great significance to develop and research renewable green energy.Among them,hydrogen energy has been widely concerned,which is due to high energy density,no carbon emissions and a wide source of raw materials and other advantages.Therefore,it is of great significance to study non-noble electrocatalysts with high activity,good stability and facile preparation method for the development of hydrogen energy industry.In this paper,the application of nickel-based electrocatalysts in hydrogen evolution reaction is taken as the research direction.The influences of heteroatom doping,construction of self-supported electrode and regulation of microstructure on transition metal nickel-based electrocatalysts are studied,and the effects of microstructure,electronic structure and surface state on hydrogen evolution reaction electrocatalytic performance are comprehensively analyzed.Furthermore,we extend the strategies of improving hydrogen evolution reaction electrocatalysts(i.e.,self-supported catalyst construction,micromorphology and defect control engineering)to other kinds of electrocatalysts on the basis of our work in this paper.Therefore,the specific content of this paper is as follows:1.Synthesis of Co-doped NiPS microflowers and its hydrogen evolution reaction performance in water splittingIn this paper,the application in hydrogen evolution reaction of Co-doped NiPS electrocatalyst with micro-flower morphology is systematically studied.Co-doped NiPS electrocatalyst material with micro-flower morphology is prepared by the combination of solvothermal method and CVD sulfuration/phosphation method in this chapter.After Co doping,CVD sulfuration and phosphation treatment,20%Co doped NiPS sample showes the best hydrogen evolution activity,presenting hydrogen evolution reaction performance with a low Tafel slope of 74.8 mV/dec and low overpotential voltage of 229.7 mV and 323.4 mV at the current densities of 10 mA/cm2 and 50 mA/cm2,respectively.The results show that the electronic structure of 20%Co-doped NiPS material is optimized by suitable Co and P doping,and the surface state and charge transfer resistance of the material are optimized.Finally,the hydrogen evolution performance of the material is improved.2.Rapid deposition of large-area amorphous Ni/NiSx film and its hydrogen evolution performance in water splittingIn order to solve the problem of using adhesive during preparing electrode with powder catalyst material,we use a simple and economical route of electrochemical deposition method to prepare amorphous Ni/NiSx composite films on nickel foam to obtain self-supporting catalyst and explore its application in hydrogen evoulution reaction and the mechanism of improving electrocatalytic performance.By systematically changing the composition of the electrolyte in the preparation process,we achieve the purpose of optimizing the material composition in the deposited film.The amorphous Ni/NiSx composite film with the optimal nickel content shows excellent HER electrocatalytic performance with overpotentials of only 43.8 mV and 134.5 mV at current densities of 10 mA/cm2 and 100 mA/cm2,respectively,as well as a Tafel slope of 79.9 mV/dec,and outstanding durability.This phenomenon can be caused by the adjustment of electrocatalyst material composition leads to the optimization of the electronic structure,the decreasing of the charge transfer resistance,and the increasing of the number of active sites due to the high electrochemical surface area,which can contribute to enhancing electrochemical performance.3.The study on d-band center regulating ultra-thin Ni5P4 nanosheets and their hydrogen evolution reaction performance in water splittingIn order to solve the material with film morphology catalyst not conducive to the increase of specific surface area and the exposure of the active site,we adopt the idea of heteroatom doping to prepare Ni5P4 electrocatalyst grown on carbon cloth to control the d-band center position by using a method of combining solvothermal and CVD phosphation in this chapter.Meanwhile,the mechanism of improving electrocatalytic performance is also explored.By systematically changing the doping element and doping ratio of heteroatom,we find that the 20%Co-doped Ni5P4 sample shows excellent electrocatalytic performance and good stability,which requires 176.8mV overpotential to reach 100 mA/cm2 current density with Tafel slope of 65.8 mV/dec in 1.0 mol/L KOH electrolyte.This is because the d-band center position can be shifted to the optimal position by doping appropriate element(Co doping)with appropriate doping ratio.Then the adsorption/desorption energy of hydrogen atom during hydrogen evolution reaction can be optimized to best value.Futhermore,the morphology of two-dimensional nanosheets can increase the number of active sites and the heterogeneous atom doping can improve the charge transfer ability by optimizing the electronic structure.These eventually improve the performance of electrocatalytic performance.4.Defect regulation of two-dimensional nanosheet electrocatalyst and its electrocatalytic performance of hydrogen evolution reactionIn order to expand the existing strategies of improving the HER performance,we successfully prepared VSe2 microflower/nanosheet electrocatalytic materials with crystal defects,controllable size and morphology on carbon cloth by using a simple chemical vapor deposition method in this chapter.Meanwhile,the mechanism of improving electrocatalytic performance is also explored.By systematically optimizing the pretreatment process parameters of carbon cloth and the growth temperature,atmosphere environment,deposition times in the chemical vapor deposition process,we find that VSe2 sample with three-dimensional microflower/nanosheet morphology shows excellent electrocatalytic hydrogen evolution performance and good stability,which requires 295.0 mV overpotential to reach 10 mA/cm2 current density with Tafel slope of 125 mV/dec in 1.0 mol/L KOH electrolyte.Due to the fact that the increasing active site number caused by small size nanosheets with abundant defect and enhaced carrier flow between the active center and the conductive substrate caused by homoepitaxy structure of micron-flower/nanosheet,VSe2 sample with three-dimensional microflower/nanosheet morphology shows good electrocatalytic performance.