Solvent effect on diffusion coefficient of some redox species in aqueous mixtures of dipolar aprotic solvents determined by rotating disc electrode technique

Diffusion coefficient of oxidant / reductant species like H + /H 2 , Br - / Br 2 , I - /I 2 , Fe + 2 / Fe + 3 , Fe (CN) 6 -4/Fe (CN) 6 -3, hydroquinone/quinone and Ferrocene / Ferricinium which are known to constitute the importantredox couples for photoelectrochemical (PEC) solar cells have been determined by rotating disc electrode technique in aqueous mixture of dipolar aprotic solvents of acetonitrile(ACN) & N,N-dimethylformamide (DMF). The larger diffusion coefficient (D) values for H + in water than those for the other ions are indicative of proton jump mechanism in the diffusion process of the ionic species in those mixed aquo-organic solvents. Further the nature of variation of D values for different redox species are interpreted in terms of change in viscosity of the medium, size of the involved ions and particularly the solvation characteristics of ACN & DMF in their aqueous mixtures.