The electrochemical redox processes in PMMA gel electrolytes—behaviour of transition metal complexes

Electrochemical properties of polymer gel electrolytes based on polymethylmethacrylate (PMMA) were studied by cyclic voltammetry and impedance spectroscopy using new solid-state PMMA–Cd–Cd2+ reference electrode. The suitable potential window of the PC–PMMA system was estimated from –0.2 to + 1.5 V versus Cd–Cd2+. New polymer gels containing ferrocene–ferricinium (Fc–Fc+) couple and other transition metal complexes were prepared by the direct polymerisation of methylmethacrylate (MMA) monomer and the solution of metal complex and supporting electrolyte in anhydrous aprotic solvent—propylene carbonate (PC). The half-wave potentials and apparent diffusion coefficients of used complexes and their dependence on the composition of the system (liquid or gel) were estimated. Time dependent electrochemical measurements showed almost three order decrease of the diffusion coefficients of ferrocene (Fc) and ferricinium (Fc+) cation from 6 × 10−5 to 2 × 10−9 cm2 s−1 during the polymerisation from the liquid to the polymer state. The results show that the PC–PMMA gel electrolyte can be described as a system of embedded solvent in the polymer network of PMMA without present monomer.