Preparation And Properties Of Novel Transition Metal Sulfide Catalysts For Hydrogen Evolution

With the consumption of fossil fuels and the aggravation of ecological environment damage,it is urgent to develop green and economical renewable energy.Therefore,abundant renewable energy sources such as wind energy and solar energy have received extensive attention,but the above-mentioned energy supply is usually limited by geographical location,climate,season and other conditions.Moreover,wind energy and solar energy is difficult to transport and store in the daily life.Hydrogen is an ideal clean energy and excellent energy storage medium.The combustion calorific value of hydrogen energy is as high as 142 MJ/kg,which is higher than that of most fossil fuels.Furthermore,hydrogen energy can achieve zero carbon emissions during use,which is considered to be one of the most potential clean energy sources in the future energy structure.The electrolysis water hydrogen production device is simple,the hydrogen production process is clean,and the energy conversion rate is high.The use of wind energy,solar energy and other clean energy sources combined with electrolysis of water technology to produce hydrogen,and then use of fuel cells and other technologies to burn and utilize hydrogen,so as to achieve the purpose of energy conversion,storage and utilization,and the whole process is basically pollution-free.It is regarded as the best way to achieve a hydrogen economy and achieve the goals of environmentally friendly and renewable sustainable development.Hydrogen evolution reaction（HER）desires the use of highly active electrocatalysts to increase the HER reaction rate and reduce the overpotential of HER,thereby accelerating the hydrogen production efficiency and reducing the electrical energy loss.In this dissertation,two highly active hydrogen evolution catalysts were obtained by a simple preparation method:MoS₂@CuCo₂S₄-Ni₃S₂/NF and CoS₂/MoS₂/CC,and the fundamental reasons for their improved HER catalytic activity in alkaline medium were explored.The main contents are as follows:（1）The composite of MoS₂and spinel-type transition metal sulfide CuCo₂S₄was realized by a three-step hydrothermal method,and a self-supporting catalytic electrode with MoS₂nanosheets grown in situ on CuCo₂S₄nanorods was prepared by using three-dimensional porous nickel foam（NF）as the substrate.CuCo₂S₄provided hydroxyl adsorption sites and cooperated with MoS₂,which provided hydrogen adsorption sites,to jointly promote the dissociative adsorption of water molecules.The rational selection of the composite material and the design of the special hierarchical structure and morphology made the catalytic electrode only need116,231,262,282 m V overpotential to reach 10,100,200,300 m A cm^-2in 1 M KOH alkaline solution,respectively.A small Tafel slope of 89.43 m V dec^-1was obtained as well.Moreover,the hydrogen evolution could be maintained at 10 m A cm^-2for 18 h,and the maintained current density was almost not attenuated,showing excellent electrocatalytic hydrogen evolution activity and stability.（2）The catalytic electrode CoS₂/MoS₂/CC with excellent hydrogen evolution performance in alkaline medium was successfully prepared by a three-step hydrothermal-electrodeposition-hydrothermal method.CoS₂and MoS₂provided hydroxyl and hydrogen adsorption sites,respectively,which synergistically promoted the dissociative adsorption of water molecules.The loading of ultra-small-sized CoS₂nanoparticles on MoS₂was beneficial to construct a large number of coupled boundaries to maximize the synergy between CoS₂and MoS₂.The electron transfer between the two phases of MoS₂and CoS₂generated to electron redistribution at the interface,which improved the intrinsic activity of the catalyst.In 1 M KOH solution,CoS₂/MoS₂/CC could reach current densities of 100 and 300 m A cm^-2with only overpotentials of 222 and 252 m V,respectively.Interestingly,CoS₂/MoS₂/CC exhibited higher activity than Pt/C at high current densities.