Solid-state voltammetry of nonaqueous proton conducting gel containing polyoxometallate redox centers

We propose a novel polvmetacrylate-based redox-conducting polymeric gel int o which silico-12-tungstic acid has been incorporated. The polyoxometallate additive (15 wt%) is entrapped as polar organic solvent solution in pores of the polymer matrix; it can also be somehow attached to the polymer struc ture. Heteropolytungstate serves both as strong acid, i.e. source of mobile protons, and well-behaved mixed-valent redox probe. It comes from ultramic roelectrode based solid state voltammetric experiments performed in the abs ence of external liquid electrolyte on bulk gel blocks that the material is characterized by well-defined redox reactions, Comparison is made to the b ehavior of silicotungstic acid single crystal. The room temperature ionic ( protonic) conductivity of the bulk gel has bee found to be equal to 1.9x10( -3) S cm(-1). Microelectrode voltammetry and potential step techniques give The following concentration of heteropolytungstate redox centers, 0.064 mo l dm(-3), and apparent diffusion coefficient, 3.7 x 10(-7) cm(2) s(-1), hav e been determined from the combination of potential step experiments perfor med in two limiting diffusional regimes, radial and linear The charge propa gation mechanism is interpreted as reflecting primarily physical diffusion of heteropolytungstate in the gel pores rather than electron hopping (self- exchange).