Study Of The Catalytic Properties Of Ionic Liquid Synthesis And Ionic Liquid Carbon Paste Electrode

Two kinds of ionic liquids, namely 1-octyl-3-methylimidazolium hexafluorophsphate ([Omim]PF6) and 1-octyl-3-methylimidazolium bis(triflylmethyl-sulfonyl)imide ([Omim]Tf2N) were prepared and characterized by IR and 1H-NMR. Nano-Ni catalyst was synthesized using [Omim]PF6 as stabilizer. X-ray diffraction analysis showed the nanoNi catalyst is composed of elemental Ni and Ni(OH)2. It was found that the prepared nanoparticles agglomerated badly during storage or transportation if ionic liquid was removed while the catalyst distributed in ionic liquid showed spherical or ellipsoidal morphology. It implied that ionic liquids could play very important roles in synthesis of inorganic nano-materials.Two carbon paste electrodes named IL-CPE and MIL-CPE were fabricated by using IL to replace liquid paraffin totally or partly. K4Fe(CN)6 was adopted as probe to study the electrochemistry behavior of IL-CPE and MIL-CPE, and the traditional carbon paste electrode M-CPE was also investigated as a comparison. The different kinetic mechanisms were found at the CPEs. Fe(CN)64-/Fe(CN)63-redox reaction is controlled by surface charge transfer at M-CPE, but diffusion control at MIL-CPE and IL-CPE. The corresponding redox current is much larger at MIL-CPE and IL-CPE than at M-CPE, nearly 8 times and 10 times, respectively, which implies that [Omim]PF6 ionic liquid has the ability to enhance charge transfer. Subsequently electrochemical performances of all kinds of CPEs in hydroquinone (H2Q) PBS buffer solution were investigated. The results show that IL-CPE has the best electrocatalytic effect toward oxidation of H2Q. The relationship of peak current Ip and square root of sweep rate and the electrochemical impedance plots indicate the oxidation of H2Q is diffusion control at IL-CPE. Diffusion coefficient D is calculated as 5.05×10-4 cm2/s according to chronoamperometry measurement, quantitatively proves H2Q has good diffusion ability at [Omim]PF6 IL-CPE. Further study reveals that anodic peak current Ipa is linear correlation to the concentration of H2Q in the range of 0.01～10 mmol/L with detection limit as 8.1×10-7 mol/L(S/N=3).Finally, nanoNi/IL-CPE and IL-nanoNi/IL-CPE were fabricated with nanoNi and IL-nanoNi as catalyst, respectively. The electrocatalytic performance of the prepared electrodes on oxidation of methanol in alkaline solution was discussed. CV curves show IL-nanoNi/IL-CPE has better catalytic effect than nanoNi/IL-CPE by comparing reversibility, reaction kinetics and peak current. This good nature could be attributed to better compatibility for IL-nanoNi than nanoNi in IL-CPE. AC impedance measurements suggest that at 0.4V the whole system acted as a simple circuit controlled by diffusion, while at 0.6V and 0.7V the system becomes complex with two time constants. It is accounted for the reaction that Ni(Ⅱ) is oxidized to Ni(Ⅲ) which leads to the oxidation of methanol. Diffusion coefficient D of methanol at IL-nanoNi/IL-CPE is calculated as 2.19×10-4cm2/s according to chronoamperometry curve, which illustrates favorable kinetic reaction characteristic.