Fabrication And Electrocatalytic Performances Of Nanomaterials Based On Transition Metals

At present,the excessive use of fossil fuels by human has caused energy shortage and serious environmental pollution.As a kind of green and clean energy,hydrogen（H₂）has been widely concerned in solving the energy crisis and environmental pollution problems.In recent years,electrochemical decomposition of water through hydrogen evolution reaction（HER）has been proven to be a promising way to obtain H₂.Commercially,water electrolysis is usually catalyzed by precious metals such as platinum（Pt）and iridium（Ir）to produce hydrogen gas,but the high price and low reserves of precious metals limit their large-scale application.Therefore,developing non-precious metal electrocatalysts with high activity and durability is a practical topic of research.In this thesis,four transition metal compound nanomaterial electrocatalysts have been constructed by using electrospinning,hydrothermal and acid etching technology,and their microscopic morphology,structure,composition and electrocatalytic properties have been systematically studied.The specific contents are as follows:（1）Carbon-based[CoS/C]//[MoS₂/C]Janus nanofibers were constructed by efficiently combining a parallel axis electrospinning technology with a dual crucible vulcanization technology.The heterogeneous structure formed by Janus fibers accelerates electron transport and the synergistic effect between bimetals makes it have excellent HER performance in 1.0 M KOH solution.At the current density of 10 m A cm^-2,the overpotential of the[CoS/C]//[MoS₂/C]catalyst is only 134 m V.[CoS/C]//[MoS₂/C]Janus nanofibers have better HER performance than the counterpart control CoS/MoS₂/C composite nanofibers,which prove the superiority of Janus structure.（2）Flexible self-supporting[Mo₂C/C]/[WO₂/C]nanofibers top-down structured Janus film was prepared by combining a uniaxial electrospinning technology with a carbonization process.Due to the high conductivity of carbon-based nanofibers,the interface effect of Janus film and the synergistic effect between metals,the catalyst exhibits excellent HER performance in alkaline electrolyte.In 1.0 M KOH solution,the[Mo₂C/C]/[WO₂/C]Janus membrane electrocatalyst only requires a low overpotential of 157 m V to obtain a HER current density of 10 m A cm^-2.The[Mo₂C/C]/[WO₂/C]nanofiber Janus membrane exhibits superior electrocatalytic performance compared to the counterpart comparative Mo₂C/WO₂/C composite fibers membrane electrocatalyst,which further prove the advantage of Janus structure in electrocatalytic reaction.（3）Flexible self-supporting[Mo₂C/C]@MoS₂nanocomposite material electrocatalyst was designed and prepared by a combining electrospinning technology with a hydrothermal method.The hierarchical heterostructure formed between one-dimensional Mo₂C/C nanofibers and two-dimensional MoS₂nanosheets accelerates electron transport,and the material has a larger electrochemical active area and excellent flexibility,making the catalyst exhibit excellent HER performance in both acidic and alkaline media.In 1.0 M KOH and 0.5 M H₂SO₄media,the[Mo₂C/C]@MoS₂electrocatalyst only requires a overpotential of 112 m V and 121 m V to reach the HER current density of 10 m A cm^-2.（4）Cu₃N/copper foam（CF）self-supported electrocatalyst was designed and constructed by an acid etching technology and subsequent nitridation process.The nanowire structure of Cu₃N can expose more active sites in the electrocatalyst.The copper foam substrate improves the overall conductivity of the material and eliminates the need for adhesives such as Nafion during testing,thus improving the catalytic performance and stability of the material.In 1.0 M KOH solution,Cu₃N/CF catalyst has excellent electrocatalytic activity for hydrogen evolution reactions,with a low overpotential of 93m V at a current density of 10 m A cm^-2.The four transition metal compound nanomaterial electrocatalysts constructed in this thesis have excellent electrocatalytic performance.The design and regulation of the morphology and structure of transition metal compounds provide theoretical and technical support for the development of highly active and low-cost transition metal compound nanomaterial electrocatalysts to replace precious metal based catalysts.