The underpotential deposition of Sn on Pt in acid media. Cyclic voltammetric and electrochemical quartz crystal microbalance studies

Abstract

This work describes the studies of tin underpotential deposition on Pt electrodes in acid media by using cyclic voltammetry and electrochemical quartz crystal microbalance techniques. The voltammetric results were analyzed and it was verified the same values of anodic charge densities for the Sn in the solutions of perchloric acid with tin sulfate or chloride. The charge density value found (380 μC cm −2), in the potential region from 0.4 to 0.8 V, was attributed to the oxidation of Sn to Sn 4+ (0.9 monolayer). The electrochemical quartz crystal microbalance results showed a mass–charge ratio of 16 g mol −1 (43 ng cm −2) and 8 g mol −1 (50 ng cm −2) in the same potential region for tin oxidation in different electrolyte solutions. These relationships are due to the formation of Sn(OH) 4 and SnO 2, respectively. The differences observed in relation to the formation of Sn(OH) 4 in solutions containing SnSO 4 and SnCl 2 were due to the presence of HSO 4 − in these solutions. In this manner the OH - can adsorb on Sn in perchloric acid media with SnSO 4. The tin hydroxide and oxide are reduced in the scanning to the potentials between 1.55 and 0.05 V.