Design And Optimization Of Copper-Based Catalysts For Electrochemical Reduction Of Carbon Dioxide

Reduction of CO2 has attracted worldwide attention because of its benefits for both environmental and energy issues. Electrochemical reduction of CO2 is an efficient, controllable and environmental process with sustainable electricity sources. Polycrystalline Cu has been proven to be the only metal that could catalyze CO2 to hydrocarbon with a high faradaic efficiency, but is still suffering from rapid deactivation, poor selectivity and large overpotential, blocking its industrial applications. Aimed at the better catalytic performance of Cu, this dissertation focused on the design of new Cu materials and elucidation of the reaction mechanisms. Our results show that Cu nanomaterials derived from controllable electrochemical preparation techniques exhibited an enhanced activity, longevity and selectivity, of CO2 reduction. The main contents and achievements are as follows:1. A reaction system for electrochemical reduction of CO2 was designed and constructed when polycrystalline Cu foil was applied as the working electrode. A considerable level of Faradaic efficiency of CH4, C2H4, HCOOH and by-product H2 from water spilitting was obtained, suggesting the rationality of this reaction system.2. Galvanostatic, potentiostatic and pulsed current techniques were applied to oxidize the polycrystalline Cu foil, and Cu oxide nanowires, nanoneedles, and nanoflowers were respectively obtained. Three Cu oxide nanomaterials showed a distinct selectivity to C2H4 production or CH4 formation. Such a selectivity difference could be owing to the varying surface morphologies of Cu oxide nanowires, nanoneedles, and nanoflowers. Besides,3D nanoflower exhibited a higher catalytic activity than 2D nanowires and nanoneedles, which resulted from 3D structure with a larger specific area and more active sites.3. Pulsed potential deposition technique was applied to prepare CuCl nanoplates. Besides, trace addtion of noble or non-noble metal would increase the quantity of nanoplates. As an electrocatalyst, the material could inhibit C2H4 formation below 1% FE, and enhanced CH4 formation simultaneously, thus improve the ratio of CH4/C2H4 in CO2 reduction. STEM characterization and DFT calculations show that the heterojunction derived from dosing second metal resulted in the elevated ratio of CH4/C2H4. This approach offers a new route for designing catalysts with a high selectivity to CH4 in CO2 reduction.4. Derived from CuO nanoflowers, the Cu nanoflowers were found to keep a high catalytic activity towards CO2 reduction for 9 h, which was a remarkable improvement compared to polycrystalline Cu. Besides, H2 production was suppressed to half of polycrystalline Cu in a wide potential window. In addition, the deposition of C on the electrodes after catalysis was directly observed. Based on the trends of catalytic products and morphplogy of catalyst changing in 9-h catalysis, the reaction pathways of electrocatalytic CO2 reduction and the involvement of the surface C in this process were elucidated.