Preparation And Catalytic Performance Of Binder-free Copper Nanowires For CO₂ Reduction

In the electrocatalytic CO₂ reduction reaction,metallic copper is the only metal catalyst that can convert CO₂ to multi-carbon products.However,there are many types of copper CO₂ electroreduction products and the product selectivity is relatively low.The preparation of oxide-derived copper catalyst is an effective method to improve product selectivity by adjusting the nanostructure of copper catalyst.Using the binderless copper nanowires catalyst in the flow cell can improve mass transfer of CO₂ and prevent the active site from being covered by the binder,which is of great significance for improving the selectivity and catalytic activity of the copper catalyst.First of all,this paper optimizes the process of electrodepositing copper and determines that in the plating solution system with 5,5-dimethylhydantoin（DMH）as the complexing agent.The copper was converted to Cu O by wet oxidation,and then the Cu O is reduced to copper nanowires by potentiostatic reduction method.The better conditions for Cu O electroreduction are that the electrolyte is 0.1 mol·L-1 KOH and the reduction potential is-0.8V（vs.RHE）.The selectivity of copper nanowires prepared by electrodepositing copper precursors in the H-type cell and the flow cell was compared for the electroreduction of CO₂.The copper nanowires have a higher selectivity to ethylene,22%.The process of electrodepositing copper is optimized.When the p H is 8.5,the bath temperature is 45°C,and the current density is 2 A?dm-2,copper obtained by constant current deposition on hydrophobic carbon paper is better as a catalyst precursor.The highest selectivity to ethylene is 38% at-0.8V（vs.RHE）.By a constant current electrodeposition method,a copper-zinc alloy was electrodeposited on a hydrophobic carbon paper as a precursor for preparing copper nanowires in a DMH plating solution system in which the molar concentration ratio of copper ions and zinc ions was 95:5.Zinc of the copper and zinc alloy was dissolved during the formation of nanowires,and are prone to generate more defects,such as grain boundaries or vacancies.The catalytic performance of copper,copper-zinc alloy and two derived nanowires obtained by electrodeposition at p H 9.0,plating bath temperature of 25℃ and current density of 2 A?dm-2 was compared.The order of selectivity to ethylene is as follows: copper-zinc alloy-derived copper nanowires>copper-derived copper nanowires>copper-zinc alloy>copper.Relative to metallic copper-derived copper nanowires,the selectivity of copper-zinc alloy-derived copper nanowires to ethylene has increased to 30%.Finally,based on the density functional theory（DFT）simulation,the adsorption energy of various intermediate products on bulk copper,copper nanowires,copper nanowires with top vacancies and copper nanowires with side vacancies was calculated.The effect of vacancies on H adsorption,H activation,water decomposition reaction and ethylene formation reaction path explain the difference in performance of copper catalysts with different structures mentioned above.Calculations show that the presence of top vacancies in the copper nanowires will increase the activity of the catalyst,reduce the relative energy for generating CO,and at the same time increase the adsorption energy of CO on the surface of the catalyst.Eventually,the selectivity of ethylene will increase.