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Start Over Author "Mascaro A" Journal electrochimica acta
27 results on '"Mascaro A"'

23. Voltammetric and rotating ring-disk studies of underpotential deposition of Ag and Cu on polycrystalline Au electrodes in aqueous H2SO4

Author

Sergio A.S. Machado, Mauro C. Santos, and Lucia H. Mascaro

Subjects
chemistry, Transition metal, Rotating ring-disk electrode, General Chemical Engineering, Inorganic chemistry, Monolayer, Electrochemistry, chemistry.chemical_element, Cyclic voltammetry, Epitaxy, Underpotential deposition, Copper
Abstract

The underpotential deposition (UPD) of Cu and Ag from sulphuric acid solutions was studied on polycrystalline Au surfaces by cyclic voltammetry at stationary and rotating ring-disk electrodes. Since the voltammetric profiles also include the surface oxide/reduction contributions, the charges were also calculated by means of the collection technique of the rotating ring-disk system. The charge values obtained from cyclic voltammetry at stationary and rotating ring-disk electrodes were 405 and 386 μC cm−2, respectively, for the oxidation of a complete monolayer of UPD Cu. The proximity of these values suggests epitaxial deposition in a two-electron reduction process. On the other hand, the charge values found for UPD Ag were 108 and 115 μC cm−2, which corresponds to the amount required for the oxidation of only half a monolayer of Ag. Since the atomic radii of the three atoms involved (Cu, Ag and Au) are very similar, the differences in the deposition models were associated with the co-adsorption of anions (sulphate or hydroxide ion) which hinders the formation of a full monolayer of Ag on polycrystalline Au surface.

Published
1998
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25. Active surface area determination of Pd-Si alloys by H-adsorption

Author

Adriana N. Correia, Lucia H. Mascaro, Luís Alberto Avaca, and Sergio A.S. Machado

Subjects
Hydrogen, General Chemical Engineering, Inorganic chemistry, Alloy, Active surface area, Analytical chemistry, chemistry.chemical_element, engineering.material, Alloy surface, Anode, Adsorption, chemistry, Desorption, Monolayer, Electrochemistry, engineering
Abstract

The active surface area of a PdSi alloy (80-20 at.%) was determined by means of the anodic charge associated to the desorption peaks of underpotential deposited hydrogen atoms. The value found was very close to that expected for a complete monolayer of PdH, considering the percentage of Pd on the surface. The results are comparable to those obtained by the classical cyclic voltammetric method of reduction of oxides grown at different inversion potentials. The agreement suggests that one full monolayer of adsorbed hydrogen is formed on the Pd portion of the alloy surface.

Published
1997
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