Electrochemical and nanoelectrogravimetric studies of the nucleation and growth mechanisms of rhenium on polycrystalline gold electrode

The nucleation and growth mechanisms for rhenium on polycrystalline gold el ectrodes from an electrolytic bath containing 0.75 mM HReO4 + 0.1 M Na2SO4, (pH 2) have been studied. The potentiostatic step technique was simultaneo usly employed with measurements of mass changes in an electrochemical quart z crystal microbalance. Scanning electronic microscopy of rhenium. electrod eposits were obtained. The mass-time transients were fitted with equations deduced from the current-time relationships of the conventional nucleation and growth models. The global equation that fitted the Deltam/t transients indicated that the electrodeposition process of rhenium started with a two- dimensional progressive nucleation (PN2D), followed by another two contribu tions. The first of them corresponds to a progressive nucleation growing un der diffusion control (PN3D(dif)) and the second contribution, which is obs erved at longer times, corresponds to a progressive nucleation under charge transfer control (PN3D(ct)). From these three contributions, the PN2D corr esponds to the charge of a monolayer and was attributed to 2D nuclei produc ed by the reduction of adsorbed perrhenate. The PN3D(dif) was the most impo rtant contribution and represented 70-80% of the mass increase. The faradic efficiency for the electrodeposition process was in the range of 12-18% fo r the experimental conditions of this study. (C) 2001 Elsevier Science Ltd. All rights reserved.