| In recent years,with the excessive consumption of fossil fuels,energy scarcity and environmental pollution problems have become increasingly serious.Therefore,it is of great importance to develop renewable and clean energy that could maintain the stable long-term development for modern society.To date,clean energy sources,including hydrogen energy,solar energy,and wind energy,have attracted much attention and been widely studied.Among them,hydrogen energy is regarded as one of the most promising alternative energy by reason of its high calorific value,high gravimetric energy density,and zero carbon footprints.Among the various methods for preparing hydrogen,electrolysis of water driven by various clean energy sources has attracted extensive attention due to the characteristics of high hydrogen purity and low energy consumption.However,the production of hydrogen by electrolysis of water requires an efficient hydrogen evolution electrocatalyst to reduce the energy barrier in the reaction,thereby reducing energy consumption and costs.Although traditional platinum-based catalysts exhibit superior catalytic activity,the large-scale application is severely restricted because of their low reserve and high cost.Therefore,it is of great significance to design and develop electrochemical hydrogen evolution catalysts with good catalytic activity based on non-precious metal materials.In this thesis,a variety of composite materials were designed and synthesized by employing several carbon materials as conductive substrate and transition metal sulfide as active substance,the electrocatalytic activity toward hydrogen evolution reaction was also tested.The thesis is mainly summarized as the following sections:1.The NiCo2S4-nitrogen-doped carbon nanofiber（NiCo2S4@NCNF）composite was synthesized by in situ oxidation polymerization,calcination and solvothermal sulfuration with bacterial cellulose as precursor,and the electrocatalytic hydrogen evolution performance was investigated.Then,the surface morphology structure and property of NiCo2S4@NCNF composite were characterized by SEM,TEM,XRD,BET and other testing method,and it was found that it has an extremely large specific surface area and a developed porous structure,which is very conducive to the diffusion of hydrogen during the electrolysis process.In addition,the nitrogen-doped carbon nanofiber structure not only improves the electrical conductivity of the electrocatalyst,but also facilitates the uniform dispersion of NiCo2S4 nanoparticles,thus increasing the active site exposure ratio of the catalyst,which makes the NiCo2S4@NCNF exhibit higher electrocatalytic hydrogen evolution reaction（HER）activity and stability.This method is based on environmentally friendly materials and has potential application value.2.The Ni（OH）2 nanosheet precursor was grown in situ on the carbon fiber paper,and then covered with Mo S2 films on the surface of Ni（OH）2 nanosheets along with the sulfuration of Ni（OH）2 through a one-step continuous heating hydrothermal process to synthesize Ni S2@Mo S2/CFP composite material.It could be found that the Mo S2 films were uniformly grown on the surface of the Ni S2 nanosheets,meanwhile,the carbon fiber paper substrate together with rational design and construction of the nanostructure effectively protect active materials from being agglomerated.Moreover,the electrical conductivity of Ni S2@Mo S2 was also greatly improved by virtue of employing carbon fiber paper as substrate.The electrochemical test results show that overpotentials of 95and 214 m V are required to deliver current densities of 10 and 100 m A·cm-2 for Ni S2@Mo S2/CFP in acidic condition,respectively.Furthermore,the Ni S2@Mo S2/CFP electrocatalyst also exhibits excellent stability of both electrocatalytic activity and morphological structure,demonstrating that the introduction of carbon fiber paper substrate plays a key role in improving the electrochemical HER performance of Ni S2@Mo S2/CFP.3.With carbon cloth（CC）as a conductive substrate,Ni（OH）2 nanosheet precursor was grown in situ by hydrothermal method.After the sulfuration process,Mo S2nanosheets were grown hydrothermally to obtain Mo S2/Ni S2/CC composite materials.It was found that the composite material has a large number of heterogeneous structures,and the electronic coupling effect between different metal sulfides could reduce the density of the electron cloud density around the active metal,which is conducive to the bonding of hydrogen atoms and further improve the electrocatalytic hydrogen evolution performance of the material.The large specific surface area of the carbon cloth substrate not only provides a large number of sites for material growth,but also fixes the growth direction of the material,which greatly improves the exposure ratio of active sites.In addition,the inherent good conductivity of carbon cloth also speeds up the electron transfer speed of the material and reduces the charge transfer resistance.4.Using carbon cloth as a conductive substrate,NiCo nanowire precursor of uniform size were synthesized in situ on carbon fiber through a simple hydrothermal process,followed by sulfuration to obtain（NiCo）S2/CC composite material.Then,Mo S2 nanosheets were grown in situ by hydrothermal method to obtain（NiCo）S2@Mo S2/CC.The one-dimensional nanowire composite structure could increase the specific surface area of the material,which is conducive to the exposure of active sites and gas diffusion.Besides,the synergistic effect between multiple heterogeneous interfaces and metals can effectively improve the electrocatalytic hydrogen evolution performance of the material.The hydrogen evolution performance of the material was investigated in 1.0 M KOH electrolyte solution.When the current density reached 10 m A·cm-2,the overpotential is 74 m V,and the Tafel slope is 54m V·dec-1.The polarization curve shows a negligible negative shift in potential after3000 CV cycles.With the overpotential is fixed at 74 m V,hydrogen can be continuously and stably produced for more than 24 h. |
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