Electrochemical behaviour of iodine redox couples in aprotic and protic RTILs: 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and ethylammonium nitrate

The electrochemical behaviour of iodine has been investigated by linear sweep voltammetry and cyclic voltammetry at a glassy carbon electrode in two ionic liquids, the first one is protic: ethylammonium nitrate (EAN) and the second one is aprotic: 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14-TFSI). The results showed that iodine yielded two reduction peaks, Pc1 and Pc2 in both ionic liquids and that reduction peaks are controlled by diffusion. The addition of an organic solvent (γ-butyrolactone or methanol) shows a dramatic effect on the electrochemical behaviour of iodine in both ILs. The Walden product values indicate that, the variations of the self-diffusion coefficient of species and ionic conductivity, versus the viscosity are inversely proportional, only in aprotic ionic liquid medium. The cyclic voltammetry iodine redox couples showed that (I2/I3-) is reversible in EAN and irreversible in Pyr14-TFSI. However, (I3-/I-) is irreversible in EAN and reversible in Pyr14-TFSI. It was also demonstrated that, (I3-) is more stable in protic ionic liquid than aprotic ones.