The Design And Performance Of Catalysts For Electrocatalytic Carbon Dioxide Reduction

The excessive use of fossil fuels increases the concentration of carbon dioxide（CO₂）in the atmosphere year by year,causing global climate change.Using CO₂as C₁resource to produce high value-added products could effectively alleviate environmental problems.Electrochemical CO₂reduction（ECR）into fuels and valuable chemicals can be powered by renewable electricity with the use of H₂O and CO₂as feedstocks,providing a feasible route to alleviate global warming and simultaneously close the carbon loop.Therefore,ECR is a promising and potential method to solve environmental problems and achieve"zero carbon"emissions,which has dual significance for environmental protection and rational utilization of carbon resources.In this thesis,we design a series of multi-scale catalysts with different compositions,morphologies and structures by constructing interfaces,coordination,introducing defects and other methods to improve the activity and selectivity of ECR to C₂H₄and CO products.The results are as follow:1.For the preparation of C₂H₄by ECR,there are still problems such as low Faradaic efficiency and low current density.Cu O@Zr O₂composites were successfully prepared by co-precipitation method.We seek to explore a synergistic effect by introducing nanoholes and tailoring the interface between Cu O and Zr O₂.Cu O@Zr O₂is highly efficient electrocatalyst for ECR to C₂H₄.In an H-type cell,electrochemical test results show that Cu O@Zr O₂delivers a faradaic efficiency（FE）as high as 47.6+0.5%towards C₂H₄formation and energy efficiency（EE）of 26.8+0.3%.The respective overall FE and FE for C₂H₄can be further improved up to 84.3+1.6%and 54.7+1.1%in a flow reactor.The Cu O@Zr O₂catalyst has excellent stability and the composition and morphology of Cu O@Zr O₂did not change in the reaction.The reasons why the Cu O@Zr O₂catalyst has excellent performance for ECR to C₂H₄are as follows.On the one hand,the introduction of Zr O₂can inhibit the occurrence of HER.On the other hand,the Zr O₂can affect the distribution of electron clouds on the Cu surface to generate Cu⁺and stabilize Cu⁺.In situ Raman results confirmed that Zr O₂can effectively stabilize Cu⁺against further reduction under CO₂reduction conditions.DFT calculation results confirmed that the incorporation of Zr O₂substantially lowers the dimerization energy of adsorbed CO intermediates,thereby boosting C-C coupling to produce C₂H₄.2.Optimizing the binding strength of *CO intermediate and lowing the*CO coupling barriers are critical to promote CO₂reduction selectively to C₂H₄.The Cu O_x@Hf O₂composite was successfully prepared by hydrothermal method,which can efficiently catalyze CO₂to C₂H₄.Tuning of CuO_x/Hf O₂interface can greatly boost CO₂adsorption and binding of*CO,thus facilitating tandem dimerization and protonation to produce C₂H₄via ECR.The relative content of Cu⁺in Cu O_x@Hf O₂can be regulated by changing the molar ratio of Cu and Hf in the precursor.CuO_x@Hf O_2（3:2）exhibits a FE of 62.6+1.3%for C₂H₄and 84.9+0.28%for C₁+C₂products at-300 m A cm^-2.Compared with Cu O,the superior catalytic performance of Cu O_x@Hf O_2（3:2）is due to the faster electron transfer rate,lower charge transfer resistance and more active sites.The performance of Cu O_x@Hf O_2（3:2）catalyst maintains good stability even after continuous electrolysis over 12.0 h.3.CO is a key raw material for the Fischer-Tropsch process,and the market demand is large.Cd-BDC MOFs catalysts were synthesized by a simple solvothermal method.The as-prepared Cd-BDC MOFs nanosheets have abundant irregular longitudinal edges and lateral size distributions between 150 nm-1.5μm,showing a two-dimensional sheet-like structure.A CO FEs exceeding 80.0%were attained over Cd-BDC MOFs in a voltage range between-0.9 and-1.1 V,approaching～88.9+0.2%at-1.0 V in CO₂-saturated 0.1 M KHCO₃solution with an H-type cell.The CO FE was further improved to 90.0%in a wide potential region from-0.16 to-1.06 V in 0.5 M KHCO₃solution using a flow reactor system.The maximum CO FE was as high as～97.6+0.3%at a low overpotential of 150.0 m V.The excellent catalytic performance of Cd-BDC MOFs is mainly attributed to the strong CO₂adsorption capacity,high electrochemical surface area,and low electrochemical impedance.4.Efficient and stable N-doped carbon supported（NC）cadmium single-atom catalysts（Cd-NC）were prepared by low-temperature pyrolysis of polyacrylonitrile and cadmium nitrate.In CO₂-saturated 0.1M KHCO₃solution with an H-type cell,the FE of CO by Cd-NC is up to90.8+1.2%at-0.9 V,which is 3.2 times that of NC at-1.1 V.In a flow-type cell,the FE of CO over Cd-NC is further improved,to a maximum of 97.2+0.9%.The Cd-NCs maintained good stability after electrolysis for up to 16.0 h.This is because Cd-NC has smaller Tafel slopes,faster electron transfer rates,and faster reaction kinetics compared to NC.