Electrochemical and in-situ Raman spectroelectrochemical study of 1-methyl-3-propylimidazolium iodide ionic liquid with added iodine

An electrochemical and in-situ Raman spectroelectrochemical study of 1-methyl-3-propylimidazolium iodide ionic liquid electrolyte (MPIm+Ix-) in the absence (x = 1) and presence (x = 3) of iodine is presented. Cyclic voltammetric measurements in combination with a platinum disk microelectrode revealed a remarkable difference before and after addition of iodine to the ionic liquid, implying the electrochemical formation of polyiodide ions (I5-) at potentials more positive than +0.6 V in the presence of an equimolar amount of iodine. To verify this presumption, we performed in-situ Raman spectroelectrochemical measurements of MPIm+I− and MPIm+I− + I2 ionic liquids in a laboratory-made spectroelectrochemical cell, while stepwise changing the potential of the working platinum disk electrode. The results obtained were in good accordance with the above-mentioned postulate about the presence of polyiodide species (I5-), and can be conveniently employed in further investigations to elucidate of the Grotthus mechanism, associated with increasing conductivity as a result of the formation of polyiodides.