The Oxidation State Regulation Of Cu-based Catalysts And The Electrochemical CO₂ Reduction

At present,converting carbon dioxide（CO₂）into fuels and chemical feedstocks through electrocatalysis has received wide reserch interest.Among the catalysts,Cu is one of the catalysts,which can electrocatalytically produce multi-carbon products(C₂₊).However,the activity and selectivity of Cu catalysts should improve further to satisfy the requiremrnts for commercialization.Although the key role of Cu oxidation state on C-C coupling has been demonstrated,it is not yet clear why the Cu⁺could exsit and how it could influence the C-C process,hindering the design of efficient Cu-based catalysts.In view of this,this thesis aims to reveal the relationship between the oxidative species,Cu⁺and C-C coupling,and clarifies that the Cu⁺-CO coordination can promote the C₂₊selectivity.The main research contents are as follows:（1）First,by using electron paramagnetic resonance,this study found that the hydroxyl radicals（^·OH）can be produced in HCO₃^-solution at ambient conditions.While introduction of KI can promote the production of^·OH radicals,which can oxidize Cu to Cu O_x.Second,Cu catalysts with a thickness of 100 nm were prepared using an ion sputtering apparatus.Under electrochemical conditions,the generated^·OH in KI+KHCO₃ electrolyte enables the oxidation of surface Cu to trace Cu⁺,which combines with I^-for the formation of Cu I thereby stabilizing the CO imtermediates.At-0.9 V_RHE,the selectivity of C₂₊increased 3.0 times than that of the control group.The concentration of I^-and the C₂₊selectivity exhibited a positive correlation.It was found that when I^--containing electrolyte was replaced with KHCO₃ solution,the I component in the Cu surface lost within 1 minute,demonstrating a dynamic relationship between the amount of Cu I and concentration of I^-in solution.This suggested that the Cu I active sites promote the C-C coupling thus improving the C₂₊selectivity.（2）In situ Raman was applied to investigate the interaction between Cu⁺and CO intermediate.Within the potential range between-0.2 to-0.7 V_RHE,the specific nonclassical complex Cu（CO）_n⁺at 2149 cm^-1 was detected,demonstrating a coordination effect between Cu⁺and CO.UV-vis spectra of CO saturated KI/Cu I solution demonstrated a significant absorption between 350 nm to 460 nm.Subsequently,in situ electrochemical desorption of CO was used to verify that this coordination effect would lead to a stronger binding of Cu⁺and CO.Finally,after introducing a small amount of Cu I（2.5 m M）into the I^--containing electrolyte for electrochemical CO reduction,the C₂₊selectivity was increased by 4.3 times.This thesis shows that the Cu⁺-CO coordination can promote the C-C coupling process thus high C₂₊selectivity in the I^--containing electrolyte.