Electrochemical aspects of tin electrodeposition on copper in acid solutions

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The electrodeposition of tin on copper electrodes was studied in sulphuric acid solutions in the 283–338 K range by employing electrochemical techniques, including electrochemical quartz crystal microbalance, and scanning electron microscopy imaging. The voltammetric profiles show the presence of both, underpotential and overpotential electrodeposition of tin. While the first process (upd) involves surface controlled reactions, the latter (opd) is under mass transport control. SEM imaging shows the formation of nanoparticles under upd conditions and larger ones in the opd potential region. Analysis of chronoamperometric response indicates an instantaneous nucleation and 2D growth coupled to an adsorption process during the early stages of underpotential deposition. Conversely, data obtained in the overpotential deposition range is consistent with the occurrence of a progressive nucleation and 3D growth under diffusion control. Electrochemical impedance experiments are characterised by Nyquist plots that exhibit two capacitive time constants and a single capacitive time constant followed by a Warburg contribution in the upd and opd potential ranges, respectively. Rotating ring-disc voltammograms display current peaks in the corresponding ring profiles associated with the formation of adsorbates on the disc during the underpotential deposition. From rotating disc data the diffusion coefficient of Sn(II) ions at the different temperatures and the corresponding diffusion activation energy were determined. A reaction scheme for the electrochemical behaviour of tin on copper electrodes in the range between the threshold potentials for the copper electrodissolution and the hydrogen evolution reactions is proposed. Mass transport of soluble species, formation of weakly and strongly adsorbed species on copper and the diffusion of tin atoms into the copper lattice are considered.