SCANNING ELECTROCHEMICAL MICROSCOPY 18 - THIN-LAYER CELL-FORMATION WITH A MERCURY POOL SUBSTRATE

Scanning electrochemical microscopic (SECM) experiments were carried out with a liquid Hg substrate. Two types of responses were observed: (i) conventional steady-state positive feedback i-d (current-distance) curves typical for SECM with a conductive substrate, i.e., a tip current growing approximately exponentially with a decrease in d as the tip approached the Hg surface and (ii) steady-state tip current independent of d after the tip penetrated the surface. The latter behavior was attributed to a thin layer of electrolyte brought inside the mercury pool by the ultramicroelectrode tip. The thickness of this layer, estimated from thin layer cell theory, was from several hundreds of nanometers to a few microns. Electrochemical measurements inside such a layer (e.g., steady-state voltammetry) yielded kinetic parameters for the heterogeneous reduction of Ru(NH3)63+ at a carbon fiber in good agreement with those obtained from steady-state voltammograms at a microdisk electrode.