Scanning electrochemical microscopy of metal/metal oxide electrodes. Analysis of spatially localized electron-transfer reactions during oxide growth

Scanning electrochemical microscopy (SECM) has been used to study the oxidation of iodide at Ta electrodes covered by a thin (similar to 2.5 nm) film of Ta2O5. SECM images of surface activity reveal that the voltammetric response of a macroscopic Ta electrode comprises the individual responses of a large number of microscopic sites, each with its own unique electrochemical behavior. Oxide film growth and metal dissolution occur simultaneously with iodide oxidation, resulting in a complex voltammetric response. The component of the voltammetric current due to iodide oxidation can be separated from the total current by SECM analysis. The growth of nanometer-thick oxide films can also be studied using SECM by monitoring the rate at which iodide is oxidized at the electrode surface.