A Study Of The Electrochemical Reduction Of Carbon Dioxide And Synthesis Of Diethyl Carbonate In Ionic Liquid Composite System

CO₂ is a carbon source which is cheap,rich and natural.It is of great significance in recycling economy and environmental protection field to recycle CO₂ organic resources.Because of the thermodynamic stability of CO₂,so it is difficult to be activated by conventional chemical methods.However,it is relatively easy to be reduced by electrochemical method with the characteristics of electron reduction,clean and environmental protection.Therefore,in order to capture and transform CO₂,it is the key to find a CO₂ absorber with low cost,high efficiency,recyclable and a good electrode.Because of the environmental friendly characteristics and excellent electrochemical performance of ionic liquids,at present,the electrochemical reduction of CO₂ is increasing in ionic liquids,but there are few studies on the catalytic mechanism of ionic liquids.The electrochemical performance of the electrolyte was enhanced by the combination of conventional ionic liquids and acetonitrile.The effect of ionic liquid as a supporting electrolyte on the electrochemical reduction of carbon dioxide was investigated.At the same time,the effects of different composition of ionic liquids on the reduction products of CO₂,current efficiency and current density were investigated.The results show that imidazole cations play a catalytic role according to the reason that if the anion portion of the ionic liquid remains unchanged,the imidazole cation EMIM⁺ is replaced by BMIM+,and the CDco increases from 18mA/cm2 to 52mA/cm2,but if the anion is only replaced,the current density is not no obvious changed.In addition,the experimental results show that the carbon dioxide reduction efficiency is related to the adsorption of imidazole cations on the surface of copper electrode by mixing experiment of BmimPF6 and EmimPF6.It is found that the copper electrode and the adsorbed cations play an important role in the reduction of carbon dioxide through the analysis of the catalytic mechanism.We added respectively three single ionic liquids [Emim]BF₄,[Bmim]BF₄,[Hmim]BF₄ and different mole ratio of compound ionic liquids in acetonitrile electrolyte in this article with copper as the working electrode to further explore the alkyl chain length of imidazole cation on the electrochemical reduction of CO₂ by cyclic voltammetry and constant potentiostatic electrolysis?CPE?and density functional theory.The cation adsorption quantity increases with the cationic size order: Emim+<Bmim+<Hmim+ on copper electrode surface.Current efficiency of CO increased from 78% to 95% with the increasing of alkyl chain length in agreement with the different cation adsorption quantity on the surface of the electrode.The current density was connected with the strength of the ion pair.Three kinds of conventional ionic liquids [Emim]BF₄,[Bmim]BF₄ and [Bmim]PF6 were also selected to combine with amino functionalized ionic liquid [NH2-amin]BF₄ which has a strong ability to absorb CO₂.CV studies show that CO₂ has a higher solubility in the composite ionic liquid of [NH2-amim]BF₄?0.9%?-[Bmim]BF₄ and the reduction peak potential shift 0.4 V positively and the peak current increases by 9 times than that of [Bmim]BF₄,which has a promising application.It is beneficial to the electrochemical reduction of CO₂ by increasing the reaction temperature from 25? to 60 ?.In the system of [NH2-amim]BF₄?0.9%?-[Bmim]BF₄,ethanol and CO₂ were used as raw materials,CH3CH2 I was used as alkylating agent,the synthesis of DEC was performed under constant conditions.The experimental results show that the optimum reaction condition used Cu as the working electrode is that the temperature is 40 ?,the electrolytic potential is-1.26V?vsAg?and the electricity is 1.5Fmol-1.Under this condition,the yield of DEC was 62.3% higher than that reported in literature.Comparative experiments were done under the same experimental conditions in order to further investigate the mechanism of electrochemical reduction synthesis of DEC by CO₂ in ionic liquids.The experimental results show that DEC is formed by the reaction of CO₂-anion produced by electrolysis and imidazole cation to form a [MIM+][CO₂^-] ion pair,which is further reacted a condensation reaction with ethanol,finally,the substitution reaction occurred with the alkylation reagent CH3CH2 I.