CYCLIC VOLTAMMETRY AT MERCURY MICROELECTRODES - EFFECTS OF MERCURY THICKNESS AND SCAN RATE

An experimental study of a series of mercury microelectrodes, prepared onto a Pt disc substrate, with mercury thickness varying from almost a film to a shrouded sphere, is presented for cyclic voltammetry invol ving amalgam formation. The range of scan rates explored was between 5 and 200 mV s(-1), so that the dominant spherical diffusion, character istic of the small electrodes, is affected to a different extent by pl anar diffusion depending on the scan rate employed. The cyclic voltamm ograms, taken from aqueous solutions containing test ions of Pb(II) an d Cd(II) with different supporting electrolytes, showed that both merc ury thickness and scan rates caused a shift toward less negative poten tials of the cathodic-anodic pattern. A detailed analysis of the typic al cyclic voltammetric parameters is done to characterize better the b ehaviour of these electrodes. An unusual trend has been observed for t he current of the stripping peak as a function of the scan rate, the t rend being either a monotone decrease or passing through a maximum dep ending on the thickness of the mercury deposit. The charge involved bo th in the cathodic and anodic scans and its dependence on scan rate an d mercury thickness allowed to ascertain the occurrence of Pt-Cd inter metallic compounds. Similarities among the results here reported with other findings obtained at mercury micro and conventional film electro des have also been discussed.