Abstract
The adsorption of anions from glyoxylic acid solutions at gold electrodes has been studied by cyclic voltammetry and in situ infrared (external reflection and ATR-SEIRAS) and Raman (SERS) spectroscopies using both Au(111) single crystals and sputtered gold thin-film electrodes. In addition, theoretical harmonic IR frequencies and intensities of glyoxylate (HCOCOO−) and hydrated glyoxylate (gem-diol, HC(OH)2COO−) species adsorbed with different geometries on Au(111) clusters have been obtained from B3LYP/LANL2DZ, 6-31+G(d) calculations. Although only hydrated glyoxylate anions have been detected in the glyoxylic acid-containing solutions, the ATR-SEIRA spectra in conjunction with density functional theory (DFT) calculations have demonstrated the existence of both adsorbed glyoxylate and hydrated-glyoxylate anions on the gold surfaces. The ratio between the coverages of these two adsorbates depends on the glyoxylic acid concentration in solution, the relative glyoxylate coverage increasing when the glyoxylic acid concentration increases. The theoretical and experimental results have confirmed bidentate bonding of the anions with their OCO plane perpendicular to the metal surface. Furthermore, the in situ infrared data have shown the formation of adsorbed (bi)oxalate and formate as intermediates in the oxidation of glyoxylate and hydrated glyoxylate to carbon dioxide. The presence of adsorbed formate has been confirmed by the SERS spectra, whereas external reflection infrared experiments have shown the formation of carbon dioxide.
Published Version
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