Preparation And Characterization Of Cobalt-based Three-Dimensional Graphene Composites And Application In Electrocatalytic Water Splitting Reaction

Hydrogen energy has become an ideal energy source to replace fossil fuels,which has the advantages of clean,renewable and high energy density.Electrocatalytic water splitting is considered as a potentially applicable technology for large-scale production of high-purity hydrogen.Pt-based catalysts have a good hydrogen evolution effect in the hydrogen evolution reaction（HER）,but Pt is expensive and scarce.Therefore,researchers have turned their attention to transition metals that are cheap and abundant in resources.Among these transition metal catalysts,cobalt-based catalysts have been widely studied by researchers for their low overpotential and excellent electrocatalytic activity.In recent years,graphene has been widely used as a carrier in the field of HER research.Among them,three-dimensional graphene has good electrical conductivity,abundant pore structure,large specific surface area,and stable physical and chemical properties.Functionalizing it can effectively improve performance.Therefore,we chose metal cobalt as the active center and 3D graphene as the carrier to prepare a series of cobalt-based 3D graphene composites.They were characterized and their application in the electrocatalytic water splitting reaction was investigated.1.Preparation,characterization and the study of electrocatalytic performance of three-dimensional graphene-supported cobalt metaphosphate electrocatalysts.Graphene oxide was prepared by Hummers method.A series of three-dimensional graphene-supported cobalt metaphosphates（Co（PO₃）₂-3D RGO）with different cobalt contents were synthesized by a facile method of hydrothermal reduction and low temperature phosphating using sodium hypophosphite as phosphorus source.A series of characterization methods were used to characterize the material.The results showed that cobalt metaphosphate was successfully loaded on3D graphene,and the material had a good 3D structure and large specific surface area.Using the HER reaction as a template reaction,the electrocatalytic performance of a series of Co（PO₃）₂-3D RGO materials was explored.The electrocatalytic performance of the material was the best when the ratio of cobalt ion and Vc was 1:1.In 0.5 M H₂SO₄ and 1 M KOH,the overpotentials of material at the current density of 10 m A cm^-2 are 176 m V and 158 m V,respectively,of which the hydrogen evolution ability and stability are good in both acidic and alkaline electrolyte solutions.The catalytic activity of material remained basically unchanged after ten hours.2.Preparation,characterization and the study of electrocatalytic performance of three-dimensional nitrogen-doped graphene supported cobalt-based bimetallic nitride electrocatalysts.In order to further improve the catalytic activity of cobalt-based 3D graphene materials,we functionalized them by nitrogen doping and bimetal loading.A series of nitrogen-doped three-dimensional graphene-supported bimetallic nitrides（Co/WN-3D NRGO,Co/VN-3D NRGO）were synthesized by a facile method of hydrothermal reduction and high-temperature calcination using dicyandiamide as nitrogen source.A series of characterization methods were used to characterize the material,and the results showed that cobalt and nitride were successfully supported on 3D graphene,and the material had an obvious 3D structure.We explored the electrocatalytic properties of a series of Co/WN-3D NRGO and Co/VN-3D NRGO materials.The electrolyte solution has good hydrogen evolution ability and good stability.The catalytic activity of materials remain basically unchanged after ten hours.