Synthesis And Electrocatalytic Water Splitting Performance Of Cobalt Selenide Based Catalysts

In recent years,environmental pollution and energy crisis have brought serious obstacles to the development of science and technology.As a sustainable energy with high energy density,hydrogen energy has attracted extensive attention.Hydrogen production by electrocatalytic hydrolysis is an effective way to produce high purity hydrogen fuel without pollution.Hydrogen production by electrocatalytic water splitting hydrolysis is an effective and free-pollution way to produce high purity hydrogen fuel without pollution.Electrocatalytic water splitting includes two half-reactions,hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.Currently,precious metal Pt based material is the most effective HER catalyst,and precious metal Ir/Ru based material owns the best performance for OER,can not be widely commercialized due to their high cost and scarce content.Therefore researchers are working to develop efficient,abundant and unique D-orbital electronic structures and adjustable atomic structure transition metal-based materials to replace precious metal catalysts.Consequently,this thesis is based on cobalt-based selenides,and aims to improve the electrocatalytic activity of the materials by means of constructing heterogeneous structures,bimetallic synergetic effects,constructing two-dimensional nanosheet structures and combining carbon substrate.Nitrogen-doped carbon nanofibers loaded transition metal-based nanoparticles were prepared by electrostatic spinning and high-temperature carbonization methods,and then the heterogeneous Co Se₂-Co O nanoparticles anchored to nitrogen-doped carbon nanofibers（Co Se₂-Co O/NCF）were synthesized by low-temperature selenization.The as-prepared nanoparticles were fixed on the conductive carbon fiber substrate,which improved the electrical conductivity of the material.At the same time,the nanoparticles were not easy to agglomerate,which was beneficial to expose more active sites.Co Se₂-Co O/NCF electrocatalysts shows good hydrogen evolution activity in both alkaline and acidic media,as well as excellent catalytic activity for oxygen evolution in alkaline media.At the same time,in alkaline medium,Co Se₂-Co O/NCF electrocatalyst material was used as both cathode and anode materials for the full water splitting hydrolysate test,Only 1.6 V is required to reach the current density of 10 m A cm^-2.In order to further explore the effects of cobalt-based bimetallic on the electro-catalytic performance on electro-catalytic performance,bimetallic nickel-cobalt based nanoparticles anchored on nitrogen-doped carbon nanofibers were prepared by electrostatic spinning and calcination heat treatment.Then,bimetallic selenide anchored on nitrogen-doped carbon nanofibers were synthesized by low-temperature selenization.The synergistic effect between bimetallic selenides enables（Ni,Co）Se₂/NCF materials to maintain good hydrogen evolution activity and good stability in acidic and alkaline media.Under alkaline conditions,（Ni,Co）Se₂/NCF require 84.4 m V overpotential to drive the current densities of 10 m A cm^-2.Under acidic conditions,the HER overpotential to afford the current densities of 10 m A cm^-2on（Ni,Co）Se₂/NCF was 77 m V.In order to further improve the electrical conductivity of electrocatalytic materials,Ni-Co-Se materials with two-dimensional nanosheet network structure were grown in situ on carbon cloth with flexible structure by hydrothermal synthesis and calcination selenization method under the condition of Ni-Co bimetallic base materials.The intrinsic metal properties of metal selenides give Ni-Co-Se good electrical conductivity and accelerate the electrochemical process.The cross-linked nanosheets form a highly open interconnection network structure and provide an effective ion and electron transport path.At the same time,the specific surface area of the material is enlarged to expand the specific surface area and promoting the full exposure of the active site.Combined with the above advantages,the HER overpotential to generate 10 m A cm^-2 current densities upon Ni-Co-Se-1/CC nanosheet under alkaline conditions was 66.8 m V.Under acidic conditions,the HER overpotential of Ni-Co-Se-1/CC nanosheet to drive the current densities of 10 m A cm^-2 is 287 m V,Ni-Co-Se-1/CC also shows good stability and durability in both acidic and alkaline media.