ELECTROCHEMICAL-BEHAVIOR OF AMINO-ACIDS ON PT(HKL) - A VOLTAMMETRIC AND IN-SITU FTIR STUDY - PART III - GLYCINE ON PT(100) AND PT(110)

The electrochemical behaviour of glycine on well-defined Pt(100) and P t(110) electrodes has been studied in an acid medium by means of cycli c voltammetry and in situ FTIR spectroscopy. The results presented in this paper and those reported previously for the Pt(111)\glycine syste m have shown that glycine oxidation is a surface structure-sensitive r eaction. Adsorbed cyanide (band around 2100 cm(-1)) and adsorbed nitri c oxide (band at 1610 cm(-1)) were the main poisoning species formed d uring the electro-oxidation of this amino acid on Pt(100). Adsorbed cy anate (2165 cm(-1)) has been also identified as an intermediate specie s during such oxidation. The formation of a carbon monoxide ad-layer w hen the Pt(100) electrode was polarised below 0.4 V in a glycine-conta ining solution has been attributed to a cyanide surface reaction to pr oduce 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. Fi nally, 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 . (C) 1998 Elsevier Science S.A. All rights reserved.