Performance And Mechanism Analysis Of The Electro-reduction CO₂ To Ethylene On Cu-Ag Catalysts

Electrochemical reduction of CO₂ emission enables the use of sustainable energy sources such as solar,wind,hydro and biomass to provide electricity and achieve a carbon cycle to solve the fossil energy crisis.The generation of its reduction products,especially C₂₊products such as ethylene,as high value-added chemicals,provides a sustainable way to achieve carbon neutrality and store renewable energy.Modulation of Cu catalyst surface structure by Ag to regulate the adsorption of interfacial key intermediate*CO to promote C-C coupling reaction to produce ethylene is currently a frontier hot topic in CO₂ electroreduction research.In this thesis,experiments were conducted to investigate the C-C coupling mechanism of Cu-Ag catalysts for the electroreduction of CO₂ to produce ethylene,and Cu-Ag catalysts were prepared and analyzed for their morphological characteristics,electrochemical properties,and selectivity.Meanwhile,the performance of pure Cu,pure Ag,and Ag oxide for the electro-reduction of CO₂ was compared and analyzed.The mesoscopic catalysts Cu,Ag,Ag₂O,and Cu-Ag were prepared by the one-pot method.The four types of catalysts were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,scanning electron microscopy-energy spectroscopy（SEM-EDS）and X-ray diffraction（XRD）.The catalyst morphologies were found to be different faceted three-dimensional structures,granular structures,top defective octahedral structures,and different faceted particles.The catalysts were confirmed as Cu（111）（200）,Ag（111）（200）,Ag₂O（111）,and Cu（111）-Cu₂O（111）-Ag（200）lattice ordered structures,the SEM-EDS of Cu₅Ag₁catalyst showed that the Cu-Ag catalyst contained copper in the oxidation state.The electrochemical performance of the catalysts illustrates that the Cu-95℃catalyst with the lowest onset potential（-0.25 V vs.RHE）,Ag₂O-4 shows the smallest diffusion resistance and the Cu₅Ag₁ catalyst provides the largest ECSA(3.82 m F cm^-2),indicating that Ag doping improves the double layer capacitor of the Cu-based catalysts and increases the electron transport capacity of the catalysts.At the same time,introducing oxidized copper into Cu₅Ag₁ at a reasonable molar ratio and obtaining a regular crystal plane structure results in excellent electrochemical performance of Cu₅Ag₁.The electro-reduction products of CO₂ were analyzed by high-performance liquid chromatography and gas chromatography at potentiostatic potential,and the products of the four types of catalysts were found to be CO,CH₄,CHOOH,and C₂H₄,with H₂ as a by-product,and Faraday efficiency was calculated.Comparing the product distribution of Ag and Ag₂O catalysts,it was found that the presence of Ag₂O increased the selectivity of CO while inhibiting the hydrogen production,and the overall product distribution was not changed;a small amount of Ag doping to Cu catalysts improved the selectivity of ethylene,with the highest Faraday efficiency（44.61%）for Cu₅Ag₁,and the increase of Ag doping decreased the ethylene selectivity.Based on the experimental results,the reaction mechanism of electrocatalytic reduction of carbon dioxide on Cu and Cu-Ag catalysts were analyzed,where hydrogen production dominated by water splitting at low potential and with a small amount of CO production on Ag atoms,then CO dimerization and hydrogenation to produce ethylene starting at potentials of-0.70 V vs.RHE.At high potentials,ethylene is the dominant selective pathway on the Cu（111）and（200）crystal planes,reaching the maximum ethylene selectivity production around-1.0 V vs.RHE,and as continue to apply a more negative potential（<-1.2 V）,it is not favor to CO dimerization,and interfacial hydrogen precipitation reoccurs as the dominant reaction.The dissertation has 54 pictures,8 tables,and 153 references.