Mechanism Of Electrochemical Capture Of CO₂ Via Chlorinated 1,4-naphthoquinone In BMIMBF₄

With the continuous progress of science and technology and the continuous consumption of fossil fuels,resulting in excessive CO2 emissions has brought great harm to the survival of mankind.Therefore,how to fix CO2 with the minimum energy on a large scale and make full use of the C resources in the CO2 has always been the focus of people's attention.In recent years,ionic liquids(ILs)have been used in the study of CO2 because of their superiority.Chlorinated 1,4-naphthoquinone compounds has not only important drug properties,but also excellent redox vectors.Usually their reaction behavior will be affected by the electron-withdrawing effects of chlorine atoms.In this dissertation,the mechanisms of electrochemical capture CO2 via 1,4-naphthoquinone(1,4-NQ),2-chloro-1,4-naphthoquinone(CNQ),2,3-dichloro-1,4-naphthoquinone(DCNQ)and 2-amino-3-chloro-1,4-naphthoquinone(ACNQ)in 1-butyl-3-methylimidazolium tetrafluoroborate(BMIMBF4)were studied by cyclic voltammetry(CV)and in-situ FT-IR spectroelectrochemistry techniques.The main work is summarized as follows:1.Study on the mechanism of electrochemical capture of CO2 via 1,4-NQ in BMIMBF4(1)In BMIMBF4,the CV curve of 1,4-NQ shows two unwell-defined couples of anodic and cathodic peaks,which is different from the two well-defined CV waves in proton inert solvent dimethyl sulfoxide(DMSO).Combined with cyclic voltabsorptometry(CVA),the electrochemical reduction process of 1,4-NQ is a reversible two-step one-electron process.(2)When the saturated CO2 was introduced in the system,the CV curve changes from two pairs redox waves to a pair of redox waves,and the current value is almost doubled.It is observed from the corresponding three-dimensional(3D)infrared spectra that the characteristic absorption peak of the intermediate 1,4-NQ·-disappears,and the IR absorption peak of CO2 is observed.Combined with the experimental data of CVA and derivative cyclic voltabsorptometry(DCVA),it is concluded that when CO2 was introduced,the 1,4-NQ is accompanied by the occurrence of chemical reaction at the same time of electrochemical reduction.The results show that 1,4-NQ-reacts with CO2 rapidly to form the initial adduct([1,4-NQ-O-CO2]·-).Subsequently,the[l,4-NQ-0-CO2]·-formed is further reduced and then quickly captures a second equivalent of CO2.2.Study on the mechanism of electrochemical capture of CO2 via CNQ and DCNQ in BMIMBF4(1)Under the condition of thin layer experiment,the CV curve of CNQ in BMIMBF4 shows two unwell-defined couples of anodic and cathodic peaks in its electrochemical redox processes,and it is concluded from CVA graph that the electrochemical reduction of CNQ is a non-reversible two-step one electron process.When CO2 was introduced,the intermediate(CNQ·-)was found in the IR 3D spectra,although only a pair of redox waves were observed on the CV graph at the scanning rata of 10 mV/s.Combined with the experimental data of CVA,it is concluded that the CNQ2-produced by CNQ via two-step reduction have a reversible chemical reaction with CO2.In addition,the reaction process is further verified by the variable scanning experiment.(2)In BMIMBF4,the CV of DCNQ is shown as two pairs of redox waves.When CO2 was introduced,two reduction waves can still be observed,even at 100%CO2 concentration.According to the results of CVA,the disappearance time of CO2 obviously lags behind the disappearance time of DCNQ.Further,combined with the experimental data of DCVA,it is concluded that DCNQ2-attacks the C center of CO2 as nucleophiles.3.Study on the mechanism of electrochemical capture of CO2 via ACNQ in BMIMBF4Under the condition of thin layer experiment,the CV curve of ACNQ in BMIMBF4 shows two unwell-defined couples of anodic and cathodic peaks in its electrochemical redox processes.When CO2 was introduced,intermediate ACNQ·-was found in the 3D spectra,although only a pair of redox waves were observed on the CV graph.Combined with the experimental data of CVA and DCVA,it is concluded that the ACNQ2-produced by ACNQ via two-step reduction have reversible chemical reaction with CO2.Further,quantitative studies have found that 1 equivalent of 1,4-NQ·-or[1,4-NQ-O-CO2]2-can capture 1 equivalent of CO2,while the reaction molar ratio between CNQ2-,DCNQ2-,ACNQ2'and CO2 is 1:1.In addition,the theoretical calculation results show that the CO2 adducts of 1,4-NQ-,[1,4-NQ-O-CO2]2-,CNQ2-,DCNQ2-and CO2 should be carbonate structure,while ACNQ2-and CO2 should form carbamate products.