Comparative Studies of the Adsorption of Cysteamine, Mercaptopropionic Acid and L-Cysteine on Ag(111)

A-H. HAMZEH, L.B. AVALLE, H.M. BAKER, H. JONES, E. SANTOS

Sevilla, Espana

Congreso; 59th International Society of Electrochemistry; 2008

The electrochemical behavior and nonlinear optical properties of cysteamine, mercaptopropionic acid and L-cysteine on Ag(111) were investigated by Cyclic Voltammetry (CV) and Second Harmonic Generation (SHG) techniques. At constant position of the crystal, the increase of the magnitude of SH signals as a function of time for cysteamine and L-cysteine was sharper and higher than the observed for mercaptopropionic acid for the same concentration in solution. Different electrochemical behaviours were observed in 10mM KClO4 pH=5 for each compound. The cyclic voltammogram in presence of L-cysteine shows a greater current density at potentials more positive than the pzc compared to the bare electrode, with the appearance of a multiplicity of peaks at potentials more negative than the pzc (-0.75 V vs SCE) assigned to a reduction/oxidation process [1, 2]. The cysteamine and mercaptopropionic acid shown only one cathodic peak (-0.79 and -0.73 V, respectively). The corresponding anodic process appear as shoulder during the positive potential scan. The SH signal for Pp polarisations, when the Ag(111) crystal is rotated around its azimuthal axis, at a fixed electrode potential of -1.2 V vs SCE, shown similar behaviour for the three compounds, only three peaks are observed in their presence and six in their absence. The adlayer formed on Ag(111) for these compounds exhibits rather insulating properties in the potential region positive to the potential of zero charge. The L-cysteine adlayer demonstrates more stability that the other compounds in a broader potential range.