The Electrochemical Reduction Of CO₂ On The Modified Gold Electrodes

With the development of social industrialization,fossil fuels were consumed on a large scale.CO₂ emissions increased,which caused serious environmental problems.In this case,the fixed conversion of CO₂ was of great significance.The use of appropriate electrode materials,suitable electrolytes,and modified the appropriate electrocatalytic active material can reduce over-potential of CO₂ and improve the Faraday electrolysis efficiency.In this paper,we selected nanomaterials?nano-gold sol and gold cluster?which had good catalytic properties and the new environmental ionic liquids as modifiers.Au₂₅,/L-Cys/Au modified electrode,GNPs/L-Cys/Au modified electrode and ionic liquid-L-Cys modified electrode were prepared respectively.Electrochemical catalytic activity on the modified electrodes and the reduction mechanism of CO₂ in acetonitrile solution and ionic liquids solution were investigated by linear sweep voltammetry and in situ IR spectroelectrochemistry.The main work was summarized as follows:1.Electrochemical reduction of CO₂ in acetonitrile solution on Au₂₅/L-Cys/Au modified electrode,GNPs/L-Cys/Au modified electrodeL-Cys/Au,GNPs/L-Cys/Au,AU₂₅/Au and Au₂₅/L-Cys/Au modified electrode were prepared by self-assembly of L-cysteine,GNPs or Au₂₅ onto gold electrode surface.The electrochemical reduction of CO₂ was studied by linear sweep voltammetry and in situ IR spectroelectrochemistry.The results of linear sweep voltammetry showed that the reduction potential was reduced by 60mV when the electrode was modified with L-cysteine.The reduction potential was reduced by 190mV when modified modified with GNPs/L-Cys.The reduction potential was reduced by 80mV when modified with Au₂₅ cluster and the reduction potential was reduced by 280mV when modified with Au₂₅/L-Cys.This indicated that Au₂₅/L-Cys/Au modified electrode had better catalytic effect than GNPs/L-Cys/Au and other modified electrodes.The results of in situ IR spectroelectrochemistry showed that CO₂^-was generated first,then a part of CO₂-was reduced to generate CO₃^2-,and the other part of CO₂^-combined with CO₂ to generate CO and CO₃^2-in the electrochemical reduction of CO₂ on Au₂₅/L-Cys/Au modified electrode.2.Electrochemical reduction of CO₂ in ionic liquid on bare Au modified electrodeThe electrochemical reduction of CO₂ in HMIMBF₄ or BMIMBF₄ were studied by linear sweep voltammetry and in situ IR spectroelectrochemistry.The mechanism of CO₂ reduction in ionic liquids and the effect of ionic liquid concentration on the electrochemical reduction of CO₂ were investigated.The reduction potential was reduced by 150mV in HMIMBF₄.The results of in situ IR spectroelectrochemistry showed that HMIM-CO₂^-was generated first,then a part of HMIM-CO₂^-generated CO,and the other part of HMIM-CO₂^-combined with CO₂ to generate CO₃^2-in HMIMBF₄ on the gold electrode.In HMIMBF₄-acetonitrile solution,the CO₂ reduction potential shifted positively with the increase of HMIMBF₄ ratio.When the proportion of HMIMBF₄ increased from 50%to 80%,the potential was almost similar.The reduction potential was reduced by 370mV in BMIMBF₄.It also showed good electrochemical reduction effect.The results of in situ IR spectroelectrochemistry showed that the reduction mechanism in BMIMBF₄ were similar to that in HMIMBF₄.And the peak potential shift amplitude was the largestwhen the ionic liquid ratio was 20%in the mixed solution.3.Electrochemical reduction of CO₂ in acetonitrile solution on BMIMBF₄-L-Cys/Au modified electrodeBMIMBF₄-L-Cys/Au modified electrode was prepared.It was found that BMIMBF₄-L-Cys/Au modified electrode reduced the charge transfer resistance and improved the electron transport efficiency.The electrochemical reduction of CO₂ on modified electrode was studied by linear sweep voltammetry and in situ IR spectroelectrochemistry.The results of linear sweep voltammetry showed that the reduction potential of CO₂ on BMIMBF₄-L-Cys modified electrode was shifted.And the concentration of L-cysteine and BMIMBF₄ affected the reduction potential of CO₂.When the concentration of BMIMBF₄ was 0.49M and the concentration of L-cysteine was 10mM,the catalytic effect was the best.The results of in situ IR spectroelectrochemistry showed that CO₂^-and CO₃^2-were generated and did not form CO.It suggested that the electrochemical reduction mechanism of CO₂ was changed,so the reaction energy was reduced.It is speculated that the CO₂^-combined with BMIM+ to produce BMIM-CO₂-on the modified electrode to reduce the energy of the reaction.The reduction of CO₂ on TEABF₄-L-Cys/Au modified electrode showed the same catalytic reduction effect and the mechanism was similar.