Preparation Of Cuprous Oxide-Derived Copper Based Catalysts For Electrocatalytic CO₂ Reduction Reaction

Electrochemical carbon dioxide reduction reaction（CO₂RR）powered by renewable energy is a very promising strategy to achieve a sustainable carbon cycle.CO₂ can be reduced to one-carbon（C₁）products or multi-carbon(C₂₊)products through different reduction pathways.Among the different products,ethanol,as a C₂₊product with a high added value,has been widely used in many fields such as biology,chemical industry,medical treatment.However,the complexity of multiple electron transfer in the process of CO₂RR results in low selectivity for the reduction products.Therefore,it is highly desired but also challenging to develop efficient and stable electrocatalysts with good selectivity for the electrochemical reduction of CO₂ to ethanol.In this thesis,based on,according to the pathway and rate-determining steps of electrocatalytic CO₂ reduction to ethanol,relatively simple methods are developed to fabricate cuprous oxide-derived copper（OD-Cu）based composite catalysts,which improve the Faradaic efficiency and selectivity of ethanol in the CO₂RR products.The main contents are as follow.（1）An electrodeposited Cu₂O/Bi films in situ converted into a composite catalyst OD-Cu/Bi（with a small amount of metallic Bi introduced into the OD-Cu film）by an electrochemical pre-reduction process to realize the modification of OD-Cu.The catalytic activity of the composite catalyst OD-Cu/Bi for CO₂RR is optimized by changing the deposition potential and deposition charge during the electrodeposition of Cu₂O/Bi.Compared with OD-Cu,the modified catalyst OD-Cu/Bi has a larger electrochemically active surface area and smaller charge transfer resistance,which accelerates the rate-determining step of CO₂ adsorption and activation,reduces the adsorption of*H,stabilizes the*CO intermediate,and therefore increases the Faradaic efficiency of ethanol in the products while suppressing the side reaction of hydrogen evolution.The optimized material,OD-Cu/Bi-5-2,exhibits the best catalytic activity for CO₂RR at-0.7 V vs.RHE with a Faradaic efficiency of 37.80%for ethanol and a decreased Faradaic efficiency of 26.44%for hydrogen.（2）A composite catalyst OD-Cu-CeO_2-x is prepared by pulse electrodeposition of CeO_2-x nanoparticles with oxygen vacancies on the OD-Cu film.The size of CeO_2-x nanoparticles is adjusted by controlling the duration of each single pulse,and the amount of the deposited CeO_2-xnanoparticles is adjusted by controlling the number of pulse cycles.The improved CO₂RR catalytic performance of the composite OD-Cu-CeO_2-xcompared to that of OD-Cu verifies that CeO_2-x nanoparticles as a cocatalyst can effectively achieve the modification of OD-Cu.The composite catalyst OD-Cu-CeO_2-x effectively enhances the adsorption and activation ability of CO₂,accelerates the generation of*CO intermediates,and stabilizes the reduction intermediates,thereby improving the Faradaic efficiency of ethanol in the product.The optimized material OD-Cu-CeO_2-x-5 exhibits the best catalytic activity for CO₂RR at-0.7 V vs.RHE with a Faradaic efficiency of 41.73%for ethanol.（3）A composite catalyst N/DC/Cu₂O@OD-Cu is designed based on the tandem catalytic mechanism and prepared by mechanically mixing the carbon defect-rich nitrogen-doped carbon（N/DC）and Cu₂O followed by an electrochemical pre-reduction of the mixture.The composite catalysts prepared with different carbon materials（with different selectivity for catalytic reduction of CO₂ to CO）or different mass ratios of Cu₂O to N/DC show different catalytic activity for CO₂RR,verifying the synergistic catalysis of carbon materials and Cu₂O@OD-Cu.In situ Raman results and DFT calculations further verify the tandem catalytic effect between carbon materials and Cu₂O@OD-Cu.The composite catalyst N/DC/Cu₂O@OD-Cu（1:5）exhibits the best catalytic activity for CO₂RR at-0.7 V vs.RHE with a Faradaic efficiency of 51.84%for ethanol and shows good stability in the long-cycle test of 8 h.