Cathodic and anodic deposition of mercury and silver at boron-doped diamond electrodes

The mechanisms of silver and mercury metal deposition On boron-doped diamon d electrodes were investigated using a prior model of three-dimensional dif fusion controlled nucleation/growth to interpret the data. The mechanism of nucleation depends upon the nucleation overpotential and metal ion concent ration. At low overpotentials, instantaneous nucleation can be observed and , at high overpotentials or concentrations, the process becomes progressive . No underpotential phenomena are observed, consistent with exceptionally w eak interaction between the deposited metal and the diamond surface. Active sites corresponding to a low density of surface sites on the electrode whi ch act as critical nuclei during the electrodeposition. Anodic reactions of silver were also investigated. It was found that the resulting product dep ends on the silver concentration in the solution. Soluble Ag(II) forms only at low concentration (<0.5 mM Ag+). Increasing concentration leads to form ation of sparingly soluble oxysalts of formula Ag7O8X, where X is NO3- or C lO4-, with voltammetric characteristics and adhesion similar to these found for cathodic metal deposits. (C) 1999 The Electrochemical Society. S0013-4 651(98)05-057-5. All rights reserved.