A Study On Electrochemical CO₂ Reduction Synergistically Catalyzed By Cu Modified With Conjugated Nitrogen Containing Small Molecules

The over-reliance of human activities on fossil fuels has produced a large amount of CO₂,which has caused irreversible damage to the earth’s ecology.Using the electricity generated by renewable energy to reduce CO₂ by electrocatalytic method can realize the artificial carbon cycle and alleviate the greenhouse effect and energy crisis.Electrocatalytic CO₂ reduction reaction（CO₂RR）has many advantages,such as environmental friendliness,low energy consumption,and adjustable product ratio,but there are also many problems to be solved urgently.On the one hand,higher polarization is required to activate CO₂.On the other hand,there is competition of hydrogen evolution reaction.As the only metal catalyst that can deeply reduce CO₂,Cu stands out from the crowd of catalysts.At the same time,there is also the challenge of product diversity.Surface modification can construct a special physical or chemical environment on the catalytic surface without changing Cu catalyst itself,and synergistically promote the electrocatalytic CO₂ reduction.Literature surveys show that most of the surface-modified molecules/polymers with synergistic catalytic effect have nitrogen-conjugated structures.Based on this,this thesis systematically studied the CO₂RR performance of different nitrogen-containing conjugated small molecules modified on the surface of Cu electrode,and explored the synergistic catalytic reaction mechanism of the modified molecules.The main research contents are as follows:1.A series of structurally similar purine molecules were used to modify the surface of Cu powder,and it was found that the selectivity of CO₂RR products was very different.The current of hydrogen evolution reaction in aqueous organic systems with dissolved purine molecules was used to reflect their synergistic proton transfer capability and correlate it with CO₂RR product selectivity in aqueous systems.It was found that the proton transfer capability was too strong,which was favorable for proton coupling to obtain H₂.If the proton transfer capability was too weak,it was favorable for C-C coupling to obtain C₂₊products.Among them,guanine had moderate proton transfer capability,which can promote the hydrogenation of CO₂ to CH₄ while suppressing hydrogen evolution reaction,selectivity was up to 42%.Through in-situ infrared spectroscopy,it was found that guanine would be deprotonated during the reaction process,and along with the configuration change of the water on the electrode surface,it could maintain a local low p H environment,which was favorable for the hydrogenation of*CO to CH₄.2.Cyclic voltammetry tests were performed on quinoxaline and its derivatives in different atmospheres（Ar,CO₂）and non-aqueous systems.We screened out 6-chloroquinoxaline and 2-hydroxyquinoxaline that were most likely to interact with CO₂in a CO₂ atmosphere,which had the most positive potential for interaction.The reduction current of 6-chloroquinoxaline was larger than that of 2-hydroxyquinoxaline.The CO₂RR performance of 6-chloroquinoxaline modified Cu electrode was better,which can significantly improve the selectivity of C₂H₄.C₂H₄ selectivity was 12.4%higher than blank Cu.3.The self-assembly of terminal thiol-modified glycine peptide chains and guanine on Cu were attempted to explore their synergistic catalytic effect on electrochemical CO₂RR.Through polarization modulation infrared,it was found that the glycine peptide chain could successfully self-assemble on Cu,but the self-assembled molecular layer fell off during the reaction.Then,referring to the self-assembly process of glycine peptide chain,we successfully self-assembled guanine into Cu powder,and it had obvious synergistic effect of catalyzing CO₂RR,which can significantly promote the generation of CH₄.CH₄ selectivity was up to 55%.