SILVER ZEOLITE-MODIFIED ELECTRODES - IMPORTANCE OF ION-EXCHANGE AND CATION SITE EFFECTS

The importance of ion-exchange kinetics with respect to the behavior of silver ion-exchanged zeolite Y-modified electrodes is discussed in this paper. In polyfunctional zeolites, such as zeolite Y, ion-exchange processes can involve intracrystalline exchange between sited and mobile cations in addition to cation counterdiffusion. Electroactive silver cations when implanted into the large channel system consisting of interconnected supercages show distinct electrochemical behavior to those occupying the small channel system of sodalite cages and hexagonal prisms. Temperature-dependent chronoamperometry and cyclic voltammetry indicate that in AgY zeolites the activation energy for counterdiffusion of silver and sodium cations in the large channel network is 30 +/- 1 kJ mol(-1). The activation energy for intracrystalline ion exchange between the large and small channel systems is 35 +/- 1 kJ mol(-1). Data recorded as a function of silver loading show that the intracrystalline exchange between small and large channel ions is slow in comparison to counterdiffusion in the large channel network.