Electrochemical behaviour of amino acids on Pt(hkl): a voltammetric and in situ FTIR study. Part III. Glycine on Pt(100) and Pt(110)

Abstract

The electrochemical behaviour of glycine on well-defined Pt(100) and Pt(110) electrodes has been studied in an acid medium by means of cyclic voltammetry and in situ FTIR spectroscopy. The results presented in this paper and those reported previously for the Pt(111) glycine system have shown that glycine oxidation is a surface structure-sensitive reaction. Adsorbed cyanide (band around 2100 cm−1) and adsorbed nitric oxide (band at 1610 cm−1) were the main poisoning species formed during the electro-oxidation of this amino acid on Pt(100). Adsorbed cyanate (2165 cm−1) has been also identified as an intermediate species during such oxidation. The formation of a carbon monoxide ad-layer when the Pt(100) electrode was polarised below 0.4 V in a glycine-containing solution has been attributed to a cyanide surface reaction to produce COads and, probably, NH4+. On Pt(110), glycine electro-oxidation produces adsorbed cyanide as a unique poisoning species. The adsorbed cyanide can be removed from the surface at potentials below 0.1 V. Finally, the presence of reversibly adsorbed glycinate anions on both Pt(100) and Pt(110) surfaces has been shown. Glycinate anions are 2-fold coordinated to the electrode surface through their carboxylate groups.