Synthesis Of Cu-based Catalysts For Electrochemical Reduction Of CO₂ To Ethylene

Rising levels of carbon dioxide（CO₂）in the atmosphere pose a number of serious environmental threats,including global warming,rising sea levels and more unstable weather.Electrochemical reduction of CO₂（CO₂ER）for high value-added products,such as carbon monoxide,formic acid,methanol,ethylene,ethanol,etc.,can reduce CO₂,and use renewable energy power.So CO₂ER is a kind of the feasible way to stimulate the circulation of carbon neutral.Ethylene is the production of fiber,rubber,plastic and plant hormone of basic chemical raw materials.Copper-based catalysts are the only metallic catalysts reported to produce multi-carbon products（including ethylene）,but achieving high selectivity and high current density remains a challenge.In order to improve the selectivity and current density of the electrochemical production of ethylene from carbon dioxide,two copper-based catalysts were designed and synthesized based on a large number of literatures.In the first one,Cu-IL/GDL electrode was prepared by one-step coprecipitation method by introducing ionic liquid which has adsorption and catalytic effect on carbon dioxide into copper electrode.The second one is aimed at the slow production of intermediate*CO on the surface of copper.Non-noble metal zinc（Zn）was introduced and Cu-Zn/GDL electrode was prepared by step pulse electrodeposition method.This study provides theoretical guidance and experimental basis for the design and development of high activity CO₂ER catalyst.Specific research contents and results:（1）Ionic liquid（IL）has strong adsorption capacity for CO₂,which can restrain competitive hydrogen evolution reaction（HER）,reduce reduction overpotential,and improve the selectivity of target products.However,at present,ionic liquid is mainly used as electrolyte,with large dosage,high cost,high viscosity,and most products are formic acid.There are a few reports about the synthesis of copper-ionic liquid composite electrode by introducing ionic liquid into electrode,but the method is complicated and unstable.In this study,one-step electrodeposition method was adopted to introduce IL,and the amino ionic liquid（AFIL）was fixed on the gas diffusion layer（GDL）in the electrodeposition process of Cu.AFIL was embedded by the deposition of Cu,so as to construct the electrocatalyst（Cu-IL/GDL）embedded by ionic liquid.X-ray powder diffraction（XRD）characterization showed that the Cu（100）/Cu（111）ratio of Cu-IL/GDL was nearly 3 fold of that for Cu/GDL,indicating that ionic liquid contributes to the formation of Cu（100）crystal plane,which has been proved to be beneficial to C-C coupling and is the key to the formation of C₂products.The reaction mechanism was investigated by material characterization（scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy（Raman）,specific surface area test（BET）,contact angle）and electrochemical characterization（linear scanning curve（LSV）,Tafel curve,cyclic voltammetry（CV）,electrochemical active area（ECSA））.It is found that the ionic liquid effectively strengthens the Cu（100）crystal plane and forms a highly synergistic"Cu-ionic liquid heterogeneous interface"combining the advantages of Cu and ionic liquid.When CO₂ is directed to the carbon fiber side of Cu-IL/GDL in H-cell,the faraday efficiency for ethylene（C₂H₄）can reach 40.67%under the synergistic action of Cu and AFIL,which is 1.78 fold of that for Cu/GDL electrode,indicating that the selectivity of ethylene is greatly improved by introducing amino ionic liquid.（2）The key step to form C₂ product is the formation of C-C bond,that is,the key intermediate*CO is coupled on the surface of Cu catalyst.But the formation rate of the key intermediate*CO on Cu is slow,and the subsequent transformation is dynamically favorable.Therefore,metal catalysts with high CO yield were introduced.Au,Ag,Ru and other precious metals improve the selectivity of copper to ethylene and ethanol,but increase the cost.Zn is cheap,but its selectivity to ethylene and ethanol is unsatisfactory.In this study,pulse method was innovatively adopted,and Zn was used as guest metal.By XRD characterization and deposition current comparison,it was confirmed that bimetallic catalyst Cu Zn/GDL was synthesized.Through electrochemical characterization（LSV,Tafel,CV,ECSA）and performance test in H-cell,it is found that under the synergistic action of Cu and Zn,the faraday efficiency of ethylene reaches 41.22%,which is 2.03 fold of that for Cu/GDL electrode.The presence of Zn increases the concentration of*CO.The selectivity of ethylene was improved,which was higher than that reported in literature.