COMBINATION OF SCANNING ELECTROCHEMICAL MICROSCOPY AND LOCAL ELECTROCHEMICAL IMPEDANCE METHOD

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The combinational use of scanning electrochemical microscopy (SECM) and other micro-electrochemical techniques, such as local electrochemical impedance method (LEIM), scanning droplet cell (SDC) and liquid-phase ion gun, was attempted to evaluate the heterogeneity of electrochemical reaction at the metal and solution interface in a scale of several μm to several ten μm. Furthermore, the performance of SECM was improved to obtain the more precise probe current images. The following results were obtained.1. Micro-disk platinum electrode for SECM was combined with micro-platinum black electrodes for LEIM. A platinum foil embedded into epoxy resin was used as a model specimen electrode. Both SECM and LEIM images could distinguish clearly between the platinum foil and epoxy resin although the lateral resolution of LEIM was several ten times as much as that of SECM.2. SDC, in which a droplet of electrolyte solution can be scanned over the specimen electrode surface, was combined with SECM. T … More he voltammetry and impedance spectra of a polycrystalline gold electrode measured with SDC have revealed that all grains have a (111) orientation but different azimuth angles. SDC was also applied to form locally anodic oxide films on titanium electrode surface. The local formation of anodic oxide film could be evaluated by SECM.3. A micro silver electrode covered with silver chloride was employed as a probe electrode of SECM. A small mount of chloride ions could be generated locally with a cathodic polarization of the microelectrode, which was named "liquid-phase ion gun". The use of liquid-phase ion gun succeeded in inducing the local breakdown of passive film on iron electrode. The critical amount of chloride ions needed for initiating the local breakdown depended on the film formation conditions, the electric field in film, and pH of solution.4. The probe current image of titanium electrode in sulfuric acid solution was measured by detecting oxygen which evolved from the electrode in parallel with film formation during anodic polarization. This probe current image coincided with the probe current image obtained with the conventional SECM measurement in which the redox system of ferrocyanide ions was employed as a mediator. Comparison between the probe current images and optical micrograph has indicated that the heterogeneity of oxygen evolution depends on the crystallographic orientation of the substrate titanium and the oxygen evolution takes place preferentially on the thinner passive film or the film with the higher donor density. Less