Synthesis Of Imidazole Ionic Liquids And The Eletrochemicial Properties Of Their Modified Carbon Paste Electrodes

In this paper, the halogenated 1,2–dimethyl-3-ethylimidazolium([edmim]Br),1,2-dimethy l-3-butylimidazolium([bdmim]Br)and 1,2-dimethyl-3–amylimidazolium([admim]Br) were f i r s t l y s y n t h e s i z e d r e s p e c t i v e l y . T h e n , t h r e e i o n i c l i q u i d s , 1,2-dimethyl-3-ethylimidazoliumhexafluorophosphate([edmi m]PF6),1,2-dimethyl-3-butylimidazoliumhexafluorophosphate([bdmim]PF6) and 1,2-dimethyl-3-amylim idazoliumhexafluorophosphate ([admim]PF6) were also synthesized respectively from [edmim]Br,[bdmim]Br and [admim]Br. The optimum synthetic conditions of the three ionic liquids were studied. The yields of [edmim]Br at 80℃,40h was 80%, [bdmim]Br at 80℃,60h was 86% and [admim]Br at 80℃,50h was 83% . The final yields of [edmim]PF6 , [bdmim]PF6 and [admim]PF6 at room temperature were 71% (35h) , 75%( 40h) and 77%(45 h),respectively.Three kinds of ionic liquids, [edmim]PF6,[bdmim]PF6 and [admim]PF6, were used to substitute paraffin to mix with graphite powder to constructe new modified carbon paste electrodes.The electrochemical properties of the new modified carbon paste electrodes were studied. Firstly, the electrochemical windows of the three modified electrodes were determined in KCl solution by CV. The results showed that the electrochemical window of EIL/CPE,BIL/CPE and AIL/CPE were 4.2V,4.0V and 3.9V respectively, wide, which were much wilder than the traditional carbon paste electrode. Secondly, the electrochemical behaviors of the three modified electrodes were investigated by using K3[Fe(CN)6] as the probe.. The results showed that the electrochemical responses of K3[Fe(CN)6] were improved with the decrease ofΔEP and with the increase of peak currents, which was due to the high conductivity of [edmim]PF6,[bdmim]PF6 and [admim]PF6.It was also deduced that the electrode processes were changed from adsorption control to diffusion control. Thirdly, the diffusion coefficients of EIL/CPE, BIL/CPE and AIL/CPE were determined by Chronocoulometry to be D1=5.87×10-6cm2/s(25℃) , D2=5.52×10-6cm2/s(25℃) and D3=5.16×10-6cm2/s(25℃) respectively, which declared that the transfer rates of electron of those three modified carbon paste electrodes were declined. Finally, the electrochemical impedance spectra (EIS) of the modified carbon paste electrodes showed that the three modified electrodes were significantly different to that of CPE. EIS of EIL / CPE, BIL / CPE and AIL / CPE were approximately straight lines, indicating that there were no electron-blocking materials on the electrodes. However, EIS of CPE had larger radius semicircle in high-frequency area indicating that the electrode process was diffusion control. Additionally, linear regression analysis were done according to the data of steady state polarization curves by computer. Cathode kinetics parameters and anode kinetics parameters of the four electrodes were showed that exchange current densities of the three modified electrodes were significantly higher than that of tradional carbon paste electrode.