Preparation Of Cu-Based Catalysts And Their Applications In CO₂ Electrocatalytic Reduction

The rapid development of industrial society has increased the consumption of fossil fuels,and the massive emission of greenhouse gases such as CO₂ has led to the deterioration of the greenhouse effect.Therefore,electrocatalytic reduction of CO₂technology can realize the recycling of carbon resources,which has remarkly energetic,environmental and economic significance.The method of electrocatalytic reduction of CO₂ has attracted wide attention from domestic and foreign researchers due to its mild reaction conditions,environmental protection,high efficiency and simple operation,etc.Cu is the only metal discovered so far that can efficiently electrocatalyze reduction of CO₂ to hydrocarbon products.However,polycrystalline Cu still faces problems such as poor selectivity,easy deactivation and high overpotential,which hinder the resource utilization and industrialization of CO₂.In this thesis,aiming at the problem of insufficient performance in the CO₂ electrocatalytic reduction reaction in the water phase system,Cu-based materials with high selectivity and stability were synthesized by efficient and simple methods.Through the design and optimization of materials,the stability of the copper-based electrodes was increased.The main research works is as follows:（1）Cu ions were impregnated on the synthesized CeO₂ supports of three different morphologies by a simple impregnation method.After high temperature H₂/Ar mixed gas reduction,Cu/CeO₂ nanorods,Cu/CeO₂ nanocubes（named x-Cu/CeO₂ NRs and x-Cu/CeO₂NCs,x represents the loading of Cu）and 10-Cu/CeO₂ nanopolyhedra（named 10-Cu/CeO₂NA）material used as a comparison were prepared.The test results showed that 10-Cu/CeO₂NRs exhibited the highest ethylene Faradaic efficiency（51.58%）,with a selectivity of 60.24%,and the catalytic stability could be maintained for about 6 hours.This type of catalyst has the catalytic performance of electrocatalytic reduction of CO₂ to C₂H₄,which is related to the following two points:（1）CeO₂ nanorods have a relatively high specific surface area,which is benifacial to the high dispersion of copper particles on their surface.（2）The CeO₂nanorods with mainly exposed（110）crystal facet tend to produce ethylene after being impregnated with copper particles.（2）On the basis of the previous chapter,it is clear that the existence of oxygen vacancies in the CeO₂ supports can improve the activity of the catalysts and the selectivity of the hydrocarbon products.The increase of oxygen vacancies increases the probability of Cu²⁺replacing Ce³⁺on the CeO₂ surface.Therefore,the CeO₂ nanorods were subjected to high temperature reduction treatment at different temperatures,and then Cu/CeO₂-T nanorods were synthesized under the condition of impregnating copper content of 10wt%（named Cu/CeO₂-T,T represents the temperature of the support CeO₂ pre-reduction treatment）.XPS results showed that after high temperature reduction pretreatment,the oxygen vacancies on the CeO₂surface had been increased,and copper particles could be evenly dispersed on the surface.The prepared catalysts were used in the electro-catalytic reduction of CO₂ system,Cu/CeO₂-500 at-1.5 V（vs.RHE）showed that the maximum Faradaic efficiency（FE）of the C₂H₄ product was 42.65%.At-1.8 V（vs.RHE）Cu/CeO₂-300 showed that the maximum Faradaic efficiency（FE）of CH₄ product was 52.68%.The stability of the two modified catalysts could still be effectively maintained.（3）Copper nanowires with a diameter of about 25-30 nm were prepared by reducing copper chloride with glucose under high temperature oil bath condition with hexadecylamine as the capping agent.In the alkaline condition of 0.1 M KOH,air was added to oxidize the Cu NWs for a certain period of time to form oxidized Cu NWs（named Cu NWs-X,X represents the oxidation time）.Under the optimal potential for forming C₂H₄（-1.1 V vs.RHE）,the selectivity of Cu NWs-6/12 to C₂H₄ was higher than that of unoxidized Cu NWs and Cu NWs-24.Cu NWs-6 showed the highest ethylene Faradaic efficiency（37.12%）,and Cu NWs-12 showed a slightly lower ethylene Faradaic efficiency（33.64%）than Cu NWs-6.The high performance of Cu NWs-6/12 was attributed to its larger electrochemically active surface area than Cu NWs and Cu NWs-24.The stability of Cu NWs-6 could only maintain for 4 h at-1.1 V（vs.RHE）,which is due to the Cu（I）species being reduced and the instability of Cu NWs during the electrocatalytic reaction.