Microgravimetric, rotating ring-disc and voltammetric studies of the underpotential deposition of selenium on polycrystalline platinum electrodes

Selenium underpotential deposition (upd) on platinum electrodes in perchloric acid solutions was analysed by cyclic voltammetry, rotating ring-disc electrode, and electrochemical quartz crystal microbalance techniques. From the results obtained for Se upd on Pt, the presence of two peaks in the positive sweep with a total charge density value of 420 μC cm−2 (found after subtraction of the charge density due to PtO from the total charge density) was observed. These results are attributed to the deposition of one Se monolayer on Pt with the occupation of two active substrate sites by each Se ad-atom. Such results were confirmed by rotating ring-disc electrode experiments. In the electrochemical quartz crystal microbalance experiments the responses for mass variations were divided in three well-defined potential regions: (A) (0.05–0.7 V), (B) (0.7–1.1 V) and (C) (1.1–1.55 V) in which the mass values of: +18, −50 and −28 ng cm−2, respectively, were described by: (i) water adsorption on previously deposited Se, (ii) dissolution of the species (Se + H2O) and (iii) dissolution of Se and formation of Pt oxide. The electrode process can be represented according to the reaction: SeO2 + 4H+ + 4e− ⇋ Seads0 + 2H2O.