Facet Control Of Copper Nanostructures For Electrocatalytic CO₂ Reduction

With the development of human society,the greenhouse effect and energy shortage are becoming serious.Electrocatalytic reduction of carbon dioxide(CO2RR)provides a new way to solve the above problems,and shows high economic and social significance.Copper,as a common metal catalyst,has attracted more and more attention because it is the only one can reduce carbon dioxide to multicarbon products with high economic value.However,the main problems that affects the application of copper based catalysts are the low selectivity for specific products and the difficulty in inhibiting side reactions.In addition,the current research on copper based catalysts are mainly focused on exploring long chain hydrocarbon products with high selectivity,few study focuses on the co-reduction of carbon dioxide and other precursors for electrochemical synthesis of organic small molecules containing heteroatoms through.The selectivity of this kind of coupling reaction is also very low so far.In view of the above issues,the article focuses on the following work.1.Firstly,the square wave potential synthesis method for Cu nanomaterials with high index crystal surface was developed to produce C2 products with high selectivity.The copper nanowires with smooth surface,uniform size and high aspect ratio were obtained by liquid phase reduction method.Then the copper nanowires with high index crystalline facets were obtained by high frequency oxidation/reduction square wave potential treatment.By adjusting the square wave potential treatment time,the surface of copper nanowires gradually evolved from smooth(110)facet to a step shape.Due to the abundant edges and the exposure of more(311)crystal faces,which provide more active sites,adsorption and coupling of the CO intermediates became easier,affording improved selectivity for multicarbon products.Under the potential of-1.1V,RHE,the total Faraday efficiency(FE)of the multicarbon products produced by high index facet exposing copper nanowires could reach 57%,in which the yield of ethylene was as high as 33%,which was nearly four times higher than that of untreated Cu nanowires.The Cu nanowires with high index crystal surface also shows obvious inhibition effect towards the side reaction of hydrogen evolution.In addition,the material have good catalytic stability,which can work stably at high current density for 6 hours.2.The synthesis of urea by co-reduction of carbon dioxide and nitrate.Through galvanic reaction,silver nanocrystals were grown on the surface of copper nanowires to obtain copper silver heterogeneous interfaces.The amount of silver precursor was optimized to adjust the size and distribution of silver nanocrystals.The obtained copper silver nanowires show uniform size,high surface roughness,large surface area and rich copper silver interfaces,leading to high electrocatalytic activity.It shows high urea selectivity in co-reduction of CO2 and nitrite.The Faraday efficiency towards urea was kept above 45%in all the testing potentials(-0.7V,RHE to-1.3V,RHE).When the applied potential was-1.1V,RHE,the selectivity of urea reached the highest value.In addition,the side reactions in the co-reduction process were obviously inhibited.Compared with the traditional electroreduction of single CO2,copper silver catalyzed co-reduction of CO2 and nitrite could synthesize urea with high selectivity at room temperature and atmospheric pressure,which provides a new direction for expanding the CO2RR to electrochemical synthesis of high value chemicals.