Studies On The Application Of Modified Silver And Copper Based Nanomaterials In Electrochemical Reduction Of Carbon Dioxide

Although consumption of fossil energy contributes to the social and economic development,it also causes excessive emission of carbon dioxide(CO₂),which brings enormous environmental questions to human beings.The sustainable energy or energy carrier is expected to deal with energy and environment crisis.By using renewable energy to converting carbon dioxide into valuable chemical products,it is an effective way to relize the cycle of carbon energy.Due to the stable thermodynamics of CO₂,the conditions for achieving high-efficiency catalytic conversion of CO₂ are still very harsh,requiring highly active catalysts to reduce energy consumption.Therefore,the technology of electrochemical reduction of CO₂ is more and more favored by scientific researchers in recent years.Single metal silver and copper have been widely used in electrochemical reduction of CO₂ because of their simple structure,good conductivity,and easy recovery.However,single metal silver and copper catalysts remain problems such as poor activity,low current density,and insufficient stability.Modified Ag,deposited Ag and Cu nanowire electrode materials were designed and synthesized through methods such as chlorination-electroreduction,silver amine electrodeposition,and increasing conductive carbonized MOF coating in this work.It was used as an electrode material in the electrochemical reduction of CO₂,and its catalytic performance was studied.The relationship between the micro-morphology structure of electrode materials and the performance of electrocatalytic reduction of CO₂ was explored.The main research contents and results are as follows:1.Through adjusting the composition of the system was by adding Fe Cl₃,Co Cl₂�2H₂O and Ni Cl₂�6H₂O,three silver chloride materials with different morphologies were synthesized and coated on carbon paper and reduced to three modified Ag electrodes.The morphology structure of the three modified Ag electrode materials and test the electrochemical reduction of CO₂ activity were characterized by XRD,SEM,TEM,XPS electrochemical technology and other means to characterize.The three modified Ag electrode materials had certain differences in structure and catalytic activities.The Ag(111)crystal plane on the spherical Ag(Ag-s/CP)electrode was most fully exposed,and the grain size was 10-60 nm.It is obtained by electroreduction of Ag Cl induced by Ni²⁺.Under the best bias potential of-1.1 V(vs.RHE),the faraday efficiency of the spherical Ag catalyst for electrocatalytic reduction of CO₂to CO reached 96%,and the current density(j)could reach 15.34 m A�cm^-2,and can maintain high catalytic activity and stability for ten hours at least.2.In the silver amine solution,five kinds of Ag catalysts with different morphologies were prepared through the constant potential deposition technology,on the CP coated with carbide Ni-MOF(Ni-C)material.The structure of electrode materials and the performance of electrochemical reduction of CO₂were measured by XRD,SEM,TEM,XPS electrochemical technology and other means.The results shown that the higher the deposition potential,the smaller the particle size of the prepared Ag nanocatalyst particles,and the more fully exposed the Ag(111)crystal planes.The dendritic Ag electrocatalyst with the smallest particle size obtained at-1.5V(vs.RHE)deposition potential had the most excellent catalytic activity.Under the best bias potential of-1.3 V(vs.RHE),the faraday efficiency of CO product of dendritic Ag electrocatalyst was 97.62%,the bias current density reached 29.4 m A�cm^-2,and it could maintain high activity and stability for 10 hours at this potential.3.Cu nanowire catalysts of different diameters were prepared by the copper chloride dihydrate reduced at different temperatures(120�C,140�C,160�C)by hydrothermal method,and investigated the performance of electrochemical reduction CO₂.The structure and morphology of Cu nanowire were characterized by XRD,SEM,TEM and XPS,and the relationship between electrode catalytic activity and the structure was explored by electrochemical technology.The results were shown that the higher the synthesis temperature,the smaller the diameter of the prepared nanowires,and the more fully exposed the Cu(200)crystal planes.Compared with the catalysts synthesized at other temperatures,the Cu nanowire catalyst synthesized at 160�C could catalyze the reduction of CO₂ to C₂H₄ more efficiently and selectively.At-1.2V(vs.RHE)potential,its faraday efficiency for electrochemical reduction of CO₂ to C₂H₄ could reach 50.8%,and the current density was 20 m A�cm^-2.After 10 h of constant potential electrolysis under the same conditions,the faraday efficiency and current density remained basically unchanged.