Design Of Copper-based Catalysts And Its Performance In Electroreduction Of Carbon Dioxide

The carbon dioxide produced by the large-scale use of fossil fuels poses a potential threat to the global climate.Using renewable energy to convert carbon dioxide into chemical industrial products with high added value by electrochemical reduction can realize the utilization of carbon dioxide.Copper,as the only metal that can convert carbon dioxide into hydrocarbons,has been widely studied.However,copper is easy to be deactivated in the catalytic process,the product selectivity is poor,and the overpotential is too large,so copper needs to be modified to improve these problems.This thesis mainly focuses on the design of copper-based catalysts with good catalytic performance.The specific research contents and results of this paper include the following two aspects:（1）It is a commonly used strategy to improve the catalytic performance by modifying the electrode surface with organic molecules.The use of negative potential cyclic voltammetry to control the morphology of the catalyst is also a common operation in the electrochemical process.Therefore,we first prepared copper oxide precursors by hydrothermal method,and then in the solvent containing polydimethyldiallylammonium chloride（PDDA）copper oxide precursors by negative potential cyclic voltammetry to prepare organic molecular modified copper based catalyst.The copper-based catalysts with different loads of organic molecules were obtained according to the different number of cycles.Among the prepared catalysts,after100 laps in the solution containing PDDA,the catalysts showed high catalytic activity for formic acid.In the mobile cell,the Faraday efficiency of formic acid was 71%at the potential of-0.6V vs.Rhe with 1 M KOH solution as the electrolyte,and the partial current density reached 114m A/cm².Through scanning electron microscopy（SEM）,it was found that the precursor of copper oxide was cracked into tens of nanometers of copper nanoparticles in the cycling process under the action of PDDA.Without the action of PDDA,copper would form nanometer dendrite structure.Combined with the peak analysis of X-ray diffraction spectrum,it is found that the micro-strain of the catalyst itself decreases first and then increases with the increase of the number of scanning turns,which affects the first increase and then decrease of the catalyst performance.Through X-ray photoelectron spectroscopy analysis,the thickness of PDDA increases with the increase of the number of cycles.The change of the thickness of PDDA molecules on the copper surface will also affect the catalytic performance.In conclusion,by comparing the relationship between the structure characterization and properties of the control group and the materials,we found that the copper-based catalyst modified by PDDA simultaneously modified the surface through organic molecules,the formation of the morphology of copper nanoparticles and the change of the micro-strain of copper nanoparticles,and other combined effects improved the selectivity of the catalyst to formic acid.The contents of this study provide ideas for the study of organic-modified copper-based catalyst and the study of the morphology change of copper-based catalyst caused by the difference of electrolyte.（2）At present,the transition metal monatomic catalyst for the electroreduction of carbon dioxide is more inclined to produce CO,but less CH₄.Here,we have prepared a carbon supported copper monatomic catalyst by simple hydrothermal reaction and acetic acid pickling,and found that it has high selectivity to methane for electroreduction of carbon dioxide.XRD,TEM,ICP-MS and other characterization methods confirmed the formation of copper monatom after pickling.By comparing the catalysts before pickling with the catalysts with different pickling degrees,it was found that the catalysts after pickling had a significant inhibitory effect on ethylene,and the selectivity of methane had been significantly improved.In particular,the selectivity of the fully pickled copper monatomic catalyst for methane in the mobile electrolytic cell is 57.3%at-1.0V vs.Rhe in the 1 M KOH electrolyte,and the methane partial current density is more than 200m A/cm².The Tafel slope analysis showed that the acid washed copper monatomic catalyst showed a higher charge transfer rate for the formation of methane.In this work,a new method of copper monatom preparation was developed.Through simple hydrothermal reaction and pickling,a monatom catalyst with good selectivity to methane could be prepared.