Synthesis And Application Of Copper Based Catalysts In Electrochemistry Reduction CO₂

In recent years,the research on electrocatalytic CO₂reduction reaction（eCO₂RR）has attracted considerable attention because it can not only solve the environmental problems caused by CO₂,but also produce high value-added products using clean energy.A large number of theoretical studies in the laboratory have proved its feasibility and prospects.In the current research on eCO₂RR,catalyst materials are the most concerned by researchers.Many catalysts can be used for eCO₂RR,but most of them are in the experimental research stage.Considering that theoretical research should be combined with actual production,we must have a deeper understanding of these different catalysts.First of all,this catalyst material should have excellent eCO₂RR catalytic performance,which is mainly reflected by the faraday efficiency（FE）,current density and long-term reaction stability that the catalyst can achieve,because this directly determines the energy efficiency and stability of the entire eCO₂RR system.Secondly,this material should be widely available in nature and easy to prepare,because the selection of catalyst will affect the operation cost of eCO₂RR system.Based on the above considerations,this paper has designed a variety of copper-based catalysts and their derivatives with copper-based catalysts as the main body.In the second chapter,four kinds of copper based oxide catalysts with different catalytic performances were obtained by one-step pyrolysis of four kinds of Cu（OH）₂precursors prepared by different methods by heating them to 500℃at a heating rate of 5℃/min in N₂atmosphere.A series of copper oxide catalysts with different morphologies were prepared by controlling the type of anions in the preparation process.Then the electrochemical performance,morphology,structure and element composition of the composite were analyzed.The main contents and research results are as follows:（1）Four different Cu（OH）₂precursors were prepared by using copper nitrate,copper sulfate,copper chloride and copper acetate as copper sources,and four different morphologies of copper oxide were prepared by one-step pyrolysis at 500℃.By observing the results of SEM images,it can be seen that after the pyrolysis of Cu（OH）₂in N₂,its pyrolysis products retain the form of precursors,highlighting the strip-like,polyhedral,flaky and flocculent structures.Na OH-assisted hydrothermal precipitation tends to form strip structure.The hydrothermal method of hydrolysis of Cu（CH₃COO）₂in the presence of glycerol leads to the synthesis of polyhedron structure.CuSO₄containing urea will lead to the direct synthesis of nano-sheet morphology.The chemical precipitation method at room temperature will produce clear and recognizable flocculent structure.（2）Experimental and theoretical studies show that oxygen vacancies can exist in CuO prepared under oxygen-poor conditions,and the introduction of oxygen vacancies may be beneficial to the adsorption and activation of CO₂molecules.Considering that the oxygen vacancy concentration can be adjusted by morphology engineering,CuO crystals with different morphologies are expected to produce different oxygen vacancy concentrations,thus affecting their catalytic performance.The existence of oxygen vacancies in the obtained CuO structure was studied by XPS characterization.Two peaks can be clearly identified in the high-resolution O1s spectrogram.The peaks at 531.7 e V（O1）and 529.7 e V（O2）can be attributed to the defect sites with low oxygen coordination and oxygen atom and metal binding,respectively.（3）By studying the performance of the synthesized materials in the electrocatalytic carbon dioxide reduction reaction,we can find that four copper oxide catalysts have certain catalytic effects in the electrocatalytic carbon dioxide reduction reaction,among which CuO-4 catalyst has the best catalytic effect.CuO-4 has a clear selectivity for carbon monoxide and long-term reaction stability,and its Faraday efficiency for generating CO reaches the maximum of 75%at-0.85 V（vs.RHE）,In addition,the overall catalytic effect is relatively stable during the stability test of up to 6 h.In the third chapter,Cu-TcPP（Fe）,5%PVP-Cu-TcPP（Fe）,10%PVP-Cu-TcPP（Fe）and 15%PVP-Cu-TcPP（Fe）were synthesized with copper nitrate trihydrate,trifluoroacetic acid,polyvinylpyrrolidone（PVP）and tetracarboxyphenol ferric chloride TcPP（Fe）as the main raw materials.A series of catalysts were prepared by controlling the amount of surfactant PVP.The electrochemical performance,morphology,structure,element composition,etc.are analyzed.The main contents and research results are as follows:（1）Fix the content of Cu（NO₃）₂·3H₂O and TcPP（Fe）,keep the atomic ratio of Cu/Fe at 2:1,control the amount of surfactant PVP,and prepare a series of Cu-Fe bimetallic organic skeletons respectively.With the constant change of the amount of surfactant,we find that when the amount of PVP reaches 15wt%,the obtained 15%PVP-Cu-TcPP（Fe）has the best catalytic effect on eCO₂RR.When the amount of PVP is further increased,There is no obvious change in the catalytic performance of eCO₂RR.（2）Surfactants can be used to assist in regulating the growth of Cu-Fe bimetallic organic skeleton,and can selectively attach to the surface of MOFS.They play a key role in the anisotropic growth of Cu-Fe bimetallic organic skeleton,resulting in the gradual transformation of the shape of Cu-Fe bimetallic organic skeleton from single sheet to hydrangea.（3）15%PVP-Cu-TcPP（Fe）has a large electrochemical active surface area,and its catalytic selectivity is also more obvious in faraday efficiency diagram.At-0.95 V（vs.RHE）,its CO faraday efficiency reached the peak of 19%among the four catalysts,and at-1.05 V（vs.RHE）,the faraday efficiency of CH₄reached the maximum of 52%.