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

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 E-1/2 = -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(center dot-) 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(center dot-) to CO2 is 1:2, forming [BQ-2CO(2)](center dot-), which is finally reduced to [BQ-2CO(2)](2)(-). The mechanism proposed is consistent with theoretical calculation since the activation energy of [BQ-CO2](center dot-) formation is much lower than that of BQ(center dot-) 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. (C) 2019 Elsevier Ltd. All rights reserved.