SILVER-ZEOLITE-MODIFIED ELECTRODES - AN INTRAZEOLITE ELECTRON-TRANSPORT MECHANISM

Ag+-A zeolite monograin layers deposited on glassy carbon electrodes show a remarkable electrochemical behavior. The number and the position of peaks and shoulders which appear in cyclic voltammograms during the first cathodic scan depend on the Ag+-exchange degree, the scan rate, and the electrolyte cations. Our observations indicate the presence of eight electrochemically distinct silver species. We discuss the mechanism of the electrochemical reactions by assuming site-specific reduction potentials, site-to-site interconversion of Ag+ ions, and formation of silver clusters, and we propose an intrazeolite electron transport mechanism. Seven peaks observed in the cyclic voltammograms are related to reduction within the zeolite in an intrazeolite process. One corresponds to an extrazeolite process, namely, the reduction of Ag+ ions on the surface of the glassy carbon electrode after ion exchange of Ag+ out of the zeolite. Four peaks out of the seven are tentatively assigned to the reduction of Ag+ at different sites in the zeolite framework and three to the reduction of silver clusters formed in the cl-cage during the cathodic scan.