Electroreduction of Chlorine Gas at Platinum Electrodes in Several Room Temperature Ionic Liquids: Evidence of Strong Adsorption on the Electrode Surface Revealed by Unusual Voltammetry in Which Currents Decrease with Increasing Voltage Scan Rates

Voltammetry is reported for chlorine, Cl2, dissolved in various room temperature ionic liquids using platinum microdisk electrodes. A single reductive voltammetric wave is seen and attributed to the two-electron reduction of chlorine to chloride. Studies of the effect of voltage scan rate reveal uniquely unusual behavior in which the magnitude of the currents decrease with increasing scan rates. A model for this is proposed and shown to indicate the presence of strongly adsorbed species in the electrode reaction mechanism, most likely chlorine atoms, Cl

Electrode kinetics and mechanism of iodine reduction in the room-temperature ionic liquid [C(4)mim][NTf2]

The fast electrochemical reduction of iodine in the RTIL l-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C 4min][NTf2], is reported and the kinetics and mechanism of the process elucidated. Two reduction peaks were observed. The first reduction peak is assigned to the process 3I2+ 2e-⇌2I 3- The second reduction peak is assigned to the process I3- + 2e- ⇌3I- A diffusion coefficient of 6.6 × 10-11 m2 s_1 (298 K) is inferred for I2 in [C4mim][NTf2] with a solubility of 1.70 mM. A mechanistic study was undertaken using a digital simulation program based on the mechanism I2 + 2e -⇌k′a⇌k′b 2I - I- +I2 ⇌k f,hom⇌kb,homI3- and simulation of the first reduction wave allowed extraction of various kinetic parameters including the diffusion coefficients for I2, I 3-, and I-, rate constants for the homogeneous process (kf,hom and kb,hom), and the heterogeneous rate constants k′a and k′b, and the associated transfer coefficients. The electrode process was found to be consistent with the following form of Butler-Volmer kinetics DI2∂[I 2]/∂z= k′ae-α-F/RT E[I 2] - k′beβF/RT E[I-] The mechanistic basis for this rate law is discussed. © 2008 American Chemical Society