Ion exchange and electron transport at methyl viologen Y modified electrodes

Cyclic voltammetry and chronocoulometry were used to study reduction of the methyl viologen dication to the cation radical at zeolite-Y-modified electrodes, Shifts in half wave potential as a function of both scan rate and MV2+ loading were shown to be due to a concentration overpotential produced by the ion exchange equilibrium at the zeolite-solution interface. Incorporation of the ion exchange-equilibrium constant for ion exchange between sodium cations and intrazeolite methyl viologen into the Nernst equation shows that equilibrium at the zeolite-solution interface is set up rapidly on the electrochemical time scale. Electron transport to the methyl viologen dication (MV2+) is also shown to occur via an extrazeolite mechanism. The electrochemical reaction rate is controlled by diffusion of methyl viologen dications from zeolite Y rather than by incorporation of charge balancing cations from the electrolyte solution. Chronoamperometric data are discussed in terms of several plausible electron transport mechanisms including percolation, coupled electron hopping, and ion exchange. The latter agrees well with the experimental data and is in keeping with rate control for an ion-exchange step from a spherical zeolite particle.