In this paper three air and water-stable room temperature ionic liquids(RTILs): N-butylpyridinium tetrafluoroborate(BPBF 4), 1-butyl-3-methylimidazolium tetrafluoroborate(BMIBF 4), and 1-ethyl-3-methylimidazolium ethyl sulfate(EMISE) were synthesized. Their electrochemical windows were measured by cyclic voltammetry at 303.15-343.15 K. The cyclic voltammograms show the order of windows which represent the electrochemical stability of RTIL is: BPBF 4BMI+--0.95 V->BP+-0.02 V-. It is very interesting that while the oxidative limit of anion BF- 4 and the reductive limit of all the cations reduce with the increase of temperature, but the oxidative limit of anion SE- increases.
The chronoampermetry was used to measure the Fe3+ diffusion coefficient of 0.031 16 mol/kg of FeCl3 in the ionic liquid, BPBF4, at GC working electrode referred to Al/Al3+ and at different scan rates over the temperature range from 293.15 to 343.15 K. Since the Fe3+ reduction reaction is a reversible process with one transfer electron, according to Cottrell′s equation, the values of diffusion coefficient of Fe3+ at different temperatures were estimated. As temperature increases, the values of the diffusion coefficient also increase owing to the diminution of the BPBF4 viscosity. The values of diffusion coefficient were fitted with the method of least-square according to Arrenius′ equation, and value of diffusion activation energy of Fe3+, ED=49.5 kJ/mol, was obtained from Arrenius′ slope.
