Diffusional cross-talk between paired microband electrodes operating within a thin film: Theory for redox couples with unequal diffusion coefficients

The diffusional cross-talk of reversible redox species with different diffusion coefficients was investigated theoretically at paired microband electrodes operating under generator-collector mode within a thin film coating. The influence of the diffusion coefficient ratio parameter onto the diffusion transport taking place in the restricted volume was investigated analytically by numerical simulations. A quantitative evaluation of the currents at the generator and the collector were performed in the conformal space fitted to the geometry of the device. The theory and the simulations show that several regimes of diffusion occur according to the diffusion length of the species. Analytical formulations, validated by simulations; were derived for most of these limiting behaviors. This model allows the determination of the concentrations of the redox species in the film, their individual diffusion coefficients, as well as the film thickness based on the currents monitored at the generator and collector. Its experimental validity is tested with a two-paired platinum microband assembly operating into a Nafion micrometric film in which the electrochemical reaction at the generator is the reduction of iron(III) cations.