Investigation on electrochemical capture of CO2 in p-Benzoquinone solutions by in situ FT-IR spectroelectrochemistry

Abstract

The electrochemical capture of carbon dioxide in p-Benzoquinone (BQ) - acetonitrile and BQ - aqueous solutions have been investigated by cyclic voltammetry (CV). Two well-defined couples of anodic and cathodic peaks in CV curve of BQ in acetonitrile solvent are substituted by one redox couple peaks with E1/2 = −0.30 V once CO2 is added. The absorption peak at 2348 cm−1 of in situ FT-IR spectroelectrochemistry indicates that CO2 is involved in the electrochemical reactions. Cyclic voltabsorptometry (CVA) and derivative cyclic voltabsorptometry (DCVA) of BQ - acetonitrile with different concentration of CO2 are investigated to demonstrate the reaction stoichiometry. The absorbance value of BQ at 2348 cm−1 is a constant during reduction process when CO2 concentration is lower than 50%. However, there is a decrease at −1.3 V potential due to the CO2 reduction when it is higher than 50%. This indicates the stoichiometry of BQ•− to CO2 is 1:1 during electrochemical capture of CO2 in CH3CN solution. Similar reaction between CO2 and BQ is observed in aqueous solution. However, the stoichiometric number of BQ•− to CO2 is 1:2, forming [BQ-2CO2]•−, which is finally reduced to [BQ-2CO2]2-. The mechanism proposed is consistent with theoretical calculation since the activation energy of [BQ-CO2]•− formation is much lower than that of BQ•− reduction. The stable structures of CO2 adduct of the reactions in aprotic and aqueous solvents are also proposed according to density functional theoretical (DFT) calculations.