Preparation And Electrochemical Hydrogen Storage Performance Of Cobalt Sulfur Alloy Composites

Cobalt based alloys have high theoretical hydrogen storage capacity and good high rate discharge performance,making them the main materials for electrochemical hydrogen storage electrodes.However,their actual discharge capacity and cycling stability need further improvement.This paper takes Co₉S₈ hydrogen storage alloy as the research object,starting from the aspects of electrode material nanomaterialization,material structure and morphology regulation,and the addition of functional materials with high catalytic activity and high conductivity.Through different methods and means,a series of Co₉S₈ composite materials with different surface morphology and organizational structure are synthesized to investigate their electrochemical hydrogen storage performance.To improve the discharge capacity,cycle stability,high rate discharge ability,and dynamic performance of Co₉S₈ hydrogen storage alloy electrode materials through different preparation techniques and doping with different active materials.The research content and results of this paper are as follows:1.The sea urchin-like porous polyphenylene（PPANI）was prepared by a simple saturated solution synthesis method.The porous polyaniline/graphene（PPANI/RGO）and porous polyaniline/carbon nanotubes（PPANI/MWCNTs）were synthesized by a solution-assisted two-step self-assembly route.The two materials were doped into the Co₉S₈ bulk alloy by ball milling method to form Co₉S₈+PPANI/RGO and Co₉S₈+PPANI/MWCNTs composites.Their discharge capacities are 701.4 m A·h·g^-1 and 689.2m A·h·g^-1,respectively.Co₉S₈ modified with special porous structure and unique morphology of PPANI material has higher discharge capacity than that modified with ordinary polyaniline.At the same time,the composite material has better high-rate discharge performance,corrosion resistance and oxygen resistance.The three-dimensional network structure formed by PPANI and carbon materials enables the electrode materials to have a more and faster electron transmission path.Therefore,the electrochemical and kinetic properties of Co₉S₈+PPANI/RGO and Co₉S₈+PPANI/MWCNTs composite electrodes have been improved.2.Using ZIF-67 as a precursor,hollow porous Co₉S₈ nanocages（H-Co₉S₈）were synthesized through a series of vulcanization processes,hydrothermal reactions,and heat treatment processes.Co₉S₈ particles（S-Co₉S₈）were prepared by hydrothermal method.In order to improve the electrochemical hydrogen storage capacity and kinetic performance of H-Co₉S₈ materials,MWCNTs and RGO were doped into H-Co₉S₈ by ball milling,respectively.Finally,H-Co₉S₈+MWCNTs and H-Co₉S₈+RGO display high discharge capacitances of 683.5 m A·h·g^-1 and 686.4 m A·h·g^-1,respectively.In addition,H-Co₉S₈/carbon materials have also achieved good high rate discharge performance,corrosion resistance,and improved kinetic properties.H-Co₉S₈ with a unique hollow structure and large specific surface area can provide sufficient electrochemical active sites to anchor hydrogen.At the same time,carbon materials with excellent conductivity can further accelerate the rate of charge transfer and improve the electrocatalytic activity of the Co₉S₈ electrode during charging and discharging.3.The hollow carbon nanofiber loaded cobalt nanoparticles（Co/HCNF）were prepared by coaxial electrospinning and annealing carbonization process.Co/HCNF was doped into Co₉S₈ matrix alloy by high-energy ball milling in the proportion of 3%,5%,7%and 10%.The results showed that the discharge capacity of Co₉S₈+5%Co/HCNF composite electrode reached 603.9 m A·h·g^-1,this may because the hollow tubular structure of HCNF can well disperse cobalt nanoparticles while providing high conductivity to prevent their aggregation.At the same time,alleviating the volume change of electrode material in the process of circulation,inhibiting the collapse of electrode material structure,and reducing the degree of electrode pulverization.In addition,cobalt nanoparticles play a catalytic role in the composite material,and the synergistic effect of the two makes the electrochemical performance of alloy electrode improved.4.Co₉S₈ polyhedral embedded porous carbon nanofiber composite（Co₉S₈/PCNF）was synthesized through electrospinning technology and subsequent vulcanization and annealing processes.Compared to Co₉S₈/CNF,the composite has a higher discharge capacity(680.1 m A·h·g^-1),and the values of I₀ and D increase while the values of R_ctdecrease,especially with a significant improvement in cycle stability.Porous carbon nanofibers help to better disperse the Co₉S₈ polyhedrons to prevent their aggregations while maintaining the stability of the material structure.On the other hand,the pore structure of PCNF is mainly mesoporous,with a larger specific surface area than CNF,providing more active sites and hydrogen diffusion channels,promoting rapid charge transfer,and improving the electrochemical and kinetic properties of electrode materials.