Kinetics of the electrodeposition of Pb⊘Sn alloys Part I.: At glassy carbon electrodes

The electrodeposition of lead, tin and lead-tin alloys on glassy carbon has been studied by electrochemical techniques. Potentiostatic I-t transients were recorded to obtain the nucleation mechanism, while cyclic voltammetry was used to characterize the system. The alloy composition was determined by differential pulse anodic stripping voltammetry. Since the redox potentials for lead and tin are similar in the non-complexing electrolyte used, HBF4, a peak-fitting program was used. In the fitting procedure the half-peak width obtained in the single metal systems were retained for the alloy, while the height and the position of the peaks were allowed to change. Structural information on the electrodeposited layers was obtained by X-ray diffraction, and scanning electron microscopy was used to determine the surface morphology. The experimental results clearly show that the deposition of lead, tin and lead-tin alloys on a glassy carbon substrate is a diffusion-controlled process with a three-dimensional (3D) growth mechanism. The nucleation is instantaneous, and the number of nucleation sites increases with increasing overpotentials, dE/d log(N-0) 60 mV decade(-1). The deposition of tin results in well-defined crystals with tetragonal shape and large areas of free glassy carbon surface. The crystallites have different sizes, which indicates fast surface diffusion of small units. In the presence of lead the microstructure of the electrodeposited tin changes drastically, resembling the microstructure of pure lead. Even small amounts of lead inhibit the deposition of tin on tin and prevent the formation of dendrites. From the stripping analysis it can be concluded that although tin and lead seem to be deposited side by side in an eutectic type alloy, some influence on the stripping potential is observed. (C) 2000 Elsevier Science S.A. All rights reserved.