Electrochemistry of zeolites on thickness shear mode oscillators

This paper describes electrochemical studies of thickness shear mode (TSM) acoustic wave oscillators coated with zeolites. The frequency response of gold on AT-cut 9 MHz quartz oscillators of silver-ion-exchanged zeolite-modified electrodes (ZMEs) under an electrochemical bias is interpreted. This is achieved using a combination of cyclic voltammetry, double-potential-step chronocoulometry (DPSC), and the frequency and resistance responses of the quartz crystal oscillators. Three ZMEs were investigated including fully exchanged Ag(12)A plus partially exchanged Ag(6.4)A and Ag(3.5)A. In all cases, the frequency response of the quartz crystal nanobalance (QCN) could only be interpreted when motional resistance changes were considered. This determines the importance of energy storage and energy dissipation of the shear wave produced by the oscillator in the zeolite film, which was affected by the deposition of silver at the zeolite-electrode-solution interface. The silver deposit formed via the reduction of silver ions originally within the zeolite phase mechanically couples the zeolite film to the underlying substrate. The resistance changes occurring during redox are thus linked to an inner interfacial slip between the zeolite film and the underlying oscillating surface. The data presented are consistent with an extrazeolite redox mechanism.