Nanocrystalline Tin‐Oxide Modified Electrodes and their Electrochemical Characterization

Nanocrystalline tin‐oxide particles were prepared as electrodes on the bases of ITO glass and AT‐cut quartz crystals (sputtered gold), respectively, and characterized for their electrochemical behavior. Experiments suggested that the SnO2 particles could induce an energy barrier to the redox reactions taking place on the electrode surface. When the amount of SnO2 exceeded ca. 10−7 mol cm−2, electrochemical activity demonstrated by the solution redox couples was entirely suppressed. Nevertheless, electrochemical impedance spectroscopic (EIS) measurements suggested that mutual communication between redox couples would still take place on the surface of SnO2. For instance, although the CV curves of Fe(CN)63‐/4‐ were completely blocked, the exchange current of Fe(CN)63‐/4‐ could still flow through the tin‐oxide modified electrode, increasing with its concentration up to 40 mM. The propagation of electrons in the SnO2 film was likely via a hopping mechanism. Electrochemical quartz microbalance (EQCM) measurements, in addition, suggested that a charge‐compensating cation (K+ or H+) uptake reaction may be induced as electrons were pumped to the Sn02 electrode, while, if electrons were removed, that could cause water desorption. Analysis based on the Frumkin adsorption isotherm showed the driving force behind the adsorption of water on SnO2 is about −2 kcal/mol. Nonetheless, the adsorbed water might face a competitive repulsion from acetonitrile when acetonitrile was used as the electrolyte medium.