Model for Solid State Voltammetry of Zeolite-Associated Species

Abstract

The electrochemical reduction/oxidation of zeolite-associated species is described from the model of Lovric and Scholz for redox conductive microcrystals and the model of Andrieux and Savéant for redox polymers. It is assumed that the reaction starts at the three-phase boundary between electrode, zeolite particle, and electrolyte. From this point, the reaction zone grows while electrons and charge-balancing cations diffuse perpendicularly along the zeolite. As a result, at short times, a Cottrell-type behavior, controlled by the diffusion of electrolyte countercations in the zeolite can be expected. At larger times, a thin-layer response in which electron hopping between adjacent redox sites acts as a rate-controlling step, should be operative. Experimental chronoamperometric data on Mn(salen)N3 (salen = trans-(R,R)-1,2-bis(salicylideneamino)cyclohexane) associated with zeolite Y in contact with different MeCN electrolytes agree with these theoretical predictions. The diffusion coefficient of electrons across the zeolite was estimated to be as long as 2 × 10-11 cm2/s whereas the diffusion coefficients of Li+ and Et4N+ were found to be close to 1 × 10-9 cm2/s. The thickness of the boundary electroactive zone of zeolite grains was estimated to be as long as 0.1−0.5 μm.