Abstract

The nucleation and growth mechanisms for rhenium on polycrystalline gold electrodes from an electrolytic bath containing 0.75 mM HReO4+0.1 M Na2SO4 (pH 2) have been studied. The potentiostatic step technique was simultaneously employed with measurements of mass changes in an electrochemical quartz crystal microbalance. Scanning electronic microscopy of rhenium electrodeposits 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 ?m/t transients indicated that the electrodeposition process of rhenium started with a two-dimensional progressive nucleation (PN2D), followed by another two contributions. The first of them corresponds to a progressive nucleation growing under diffusion control (PN3Ddif) and the second contribution, which is observed at longer times, corresponds to a progressive nucleation under charge transfer control (PN3DCT). From these three contributions, the PN2D corresponds to the charge of a monolayer and was attributed to 2D nuclei produced by the reduction of adsorbed perrhenate. The PN3Ddif was the most important contribution and represented 70-80% of the mass increase. The faradic efficiency for the electrodeposition process was in the range of 12-18% for the experimental conditions of this study. © 2001 Elsevier Science Ltd. All rights reserved.