Study On Modification Of Copper-based Electrodes For Selectively Catalytic Reduction Of CO₂

At present,more than 80%of the energy consumption in the world comes from fossil fuels.The burning of fossil fuels will produce a large amount of harmful gases.In addition,fossil fuels are non-renewable.Therefore,in the long-term,in order to alleviate environmental pollution,prevent imminent energy shortages,it is necessary to use clean and renewable energy,such as solar,wind,geothermal,and biomass to replace fossil fuels on a large scale,and develop new,low-cost,environmentally friendly energy conversion and storage system.In principle,carbon dioxide can be available for free,and be converted into a large number of valuable products,which is a promising way to reduce carbon dioxide emissions and will become a means of renewable energy storage.In recent years,the conversion of carbon dioxide(CO2)into more valuable chemicals has aroused widespread research interest.Electrochemical reduction of carbon dioxide can produce a wide range of reduction products.Among them,methane,as an important C1 product of CO2 reduction reaction,is the basic organic chemical raw material for industrial production such as ethylene,acetylene,and methanol.Ethylene is a very promising since it is widely used in the production of polymer plastics.As a C2 reduction product,its commercial value and energy density are much higher than C1 products(CO,HCOOH,etc.).Copper has become the focus of attention because it is the only pure metal that converts carbon dioxide into products that require more than two electron transfers(collectively referred to as further reduction products or>2e-products).However,there are still unsolved obstacles in the conversion of CO2 to hydrocarbons by copper-based catalysts,which mainly include:numerous reduction products and poor selectivity;overpotential needed to activate CO2 reduction reaction(CO2RR)is too high and the catalyst is easily deactivated.In orde to address the issues,herein,copper-based eletrodes have been preprared and modified through an economical and simple one-step electrodeposition method for methane and ethylene formation with good stability.This thesis mainly includes two parts,which are introduced as follows:1.Preparation of F-doped Cu2O thin film and its electrocatalytic CO2 reduction performanceF-doped Cu2O film is prepared by a simple and convenient one-step electrodeposition method.The doping of halogen element F improves the selectivity of C2 product ethylene.By changing the concentration ratio of F/Cu,the best sample of F-doped Cu2O(FC 4:3)is obtained.Compared with pure Cu2O film,the Faraday efficiency of C2H4 increases by nearly 3 times,and its value is about 28%.besides,the stability of the sample has also been significantly improved compared with that of the control sample.After 12 hours,the activity attenuation was smaller.The F doped sample has larger surface area so that more active sites may be exposed,which is conducive to the adsorption and reduction of CO2.In addition,the incopration of F changes the electronic structure of Cu2O.It is well known that F atoms have strong electronegativity.When the ion F is doped into the Cu2O lattice to replace the O ion,the charge distribution of Cu will change,resulting in the asymmetric distribution of positive and negative charges,forming a strong polar group with Cu,which has an impact on the activity of CO2 reduction.In addition,as the reduction time increases,the partial escape of F leads to a slight decrease in the stability of CO2 reduction.2.Preparation of organics modified Cu electrode for catalytic reduction of CO2 to methaneThe organics-modified Cu electrocatalyst is prepared by one-step electrodeposition method with the presence of sodium citrate dihydrate.We found that through the addition of organic salt of sodium citrate dihydrate,the morphology of the Cu surface can be effectively controlled,and its electrochemically active specific surface area increases,so that more active sites are exposed on the surface.Secondly,the organic functional groups are adsorbed on the surface of the catalyst.Finally,compared with the pure Cu flakes of the comparative sample,the surface of the Cu electrocatalyst modified with organics is more hydrophobic than that of the control sample,which inhibits the competition reaction of hydrogen evolution reaction)and promoting the CO2 adsorption and reduction reactions.Thus,the Faraday efficiency of its C1 product methane is improved.At the same time,its activity is only slightly attenuated in the long-term stability test,which shows good CO2 reduction activity and selectivity for the sample.