Structural and electrical studies of a sol-gel derived nanocomposite ionic liquid based on positively charged polysilsesquioxane and iodide

A new sol-gel precursor, based on 1-methyl-3-[3-(trimethoxy-λ4-silyl)propyl]imidazolium iodide (MTMSPI+I−), was synthesized and investigated as a potential novel quasi-solid-state ionic liquid redox electrolyte for dye-sensitized photoelectrochemical cells of the Graetzel type. MTMSPI+I− was hydrolyzed with acidified water and the reaction products of the sol-gel condensation reactions were assessed with the help of 29Si NMR and infrared spectroscopic techniques, which revealed that the aged MTMSPI+I− sols consisted of a positively charged polyhedral cube-like silsesquioxane and iodide/triiodide species. The addition of iodine increased the specific conductivity of the non-hydrolyzed and hydrolyzed MTMSPI+I−, which was attributed to the formation of triiodide ions and demonstrated from Raman spectra measurements. Steady-state voltammetric measurements at a Pt disc microelectrode, performed for the hydrolyzed MTMSPI+I− and MTMSPI+I− + I2 sols, revealed changes in the apparent diffusion coefficients (Dapp) during the course of transformation of the ionic liquid from a liquid to a quasi-solid-state.