Electrochemical CO₂ Capture Mechanism And Product Analysis Of Benzoquinone And Its Four Derivatives

The continuous unreasonable emission of carbon dioxide（CO₂）directly leads to global warming,one of the main causes of the greenhouse effect.How to effectively reduce CO₂concentration has attracted much attention.Electrochemical reduction is one of the most popular methods to capture CO₂.The carbonyl group of quinone compound（Q）is highly reductive and Q undergoes a two-step single electron transfer process in an aprotic solvent.The difference of substituents on the Q benzene ring will affect its redox potential and the mechanism and process of capturing CO₂.The mechanism of carbon dioxide capture by electroreduction of quinone derivatives in proton-inert solvents was investigated,and the influence of electron-withdrawing and electron-donating groups on the mechanism of carbon dioxide capture by Q electrochemistry was studied.The main contents are as follows:1.The electrochemical capture of CO₂by BQ in acetonitrile solution was studied by cyclic voltammetry（CV）,field infrared spectroscopy and potentiostatic electrolysis.The results showed that BQ exhibited two pairs of redox peaks under the condition of N₂in acetonitrile solution.In the presence of CO₂,there is only a pair of redox peaks.According to the field infrared spectroscopy analysis,CO₂is captured by the monovalent anion radical BQ^·-in the two-step single electron transfer process,which indicates that BQ^·-can be used as a nucleophile to capture CO₂.Then the precipitation products of CO₂captured by BQ electrochemistry were obtained by potentiostatic electrolysis.According to FTIR comparison analysis,the product was obviously different from BQ,indicating that BQ and CO₂reacted in the electrochemical reduction process.According to the results of ¹H-NMR,¹³C-NMR and elemental analysis,it can be deduced that the product is the adduct of chemical reaction between BQ and CO₂,the stoichiometric ratio of CO₂captured by BQ electrochemical is 1:2,and the nucleophilic attack on CO₂is the oxygen on the carbonyl group of BQ,forming a relatively stable carboxylic acid structure.After acidifying the product,it was found that the product was transformed into p-phenol.This further proves the rationality of the structure inference of CO₂products captured by BQ electrochemistry.2.According to the findings of electrochemical capture of CO₂by BQ,the electrochemical capture of CO₂by 2,6-dichlorobenzene quinone（DCBQ）,tetrachlorobenzene quinone（TCBQ）,2,3-dicyano-5,6-dichlorobenzene quinone（DDQ）containing electron-withdrawing groups was studied.Among them,DCBQ and TCBQ of-Cl substituted group are generated divalent anions DCBQ^2-and TCBQ^2-to capture CO₂after two-step single electron transfer.DDQ follows the EE electron transfer mechanism under N₂condition,but no CO₂disappearance and generation peak can be observed from CV and IR spectra after the addition of CO₂,indicating that DDQ cannot capture CO₂electrochemically.DCBQ and TCBQ chemically captured CO₂products were characterized and found to react with CO₂in the process of electrochemical reduction,respectively.The product structure was carboxylic acid structure adduct.3.The electrochemical capture of CO₂in dimethyl sulphoxone（DMSO）solution with electron donating group TMBQ was further studied.It was found that TMBQ exhibited two pairs of redox peaks in DMSO solution under N₂condition.With the increase of CO₂concentration,the potential of the second reduction peak gradually shifted positively and finally overlapped with the first reduction peak.It was found that CO₂was captured by TMBQ anion radical TMBQ^·-and bivalent anion TMBQ^2-,respectively,and stable carboxylic acid structure compounds were formed according to field infrared spectrochemical analysis.The stoichiometric ratio of CO₂capture by TMBQ is 1:2,and the transfer mechanism of the reaction process follows（E-C-E-C）.The product of potentiostatic electrolysis was characterized and analyzed,and the product structure was carboxylic acid structure adduct,which was consistent with the analysis of field infrared spectroscopy and electrochemical method.