Theoretical and Spectroelectrochemical Studies on the Adsorption and Oxidation of Glyoxylate and Hydrated Glyoxylate Anions at Gold Electrodes

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) 2 COO -) 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.

Advances in surface-enhanced vibrational spectroscopy at electrochemical interfaces

“…For example, Xu and co-workers studied the electroreduction of CO 2 on Cu electrodes and reported that CO and H are able to co-adsorb at low overpotentials, but H can partially displace CO due to stronger Cu-H binding [144]. EC-SEIRAS has also found recent application in the study of photochemical reactions [147,148], electrochemical processes in ionic liquids [149,150], and a wide range of adsorption phenomena at metal electrodes [151][152][153][154][155][156][157]. Rodes et al monitored the adsorption of glycine on Au thin films using EC-SEIRAS and confirmed that the preferential binding mode is in a bidentate configuration (Figure 7(b)) and that co-adsorption of perchlorate anions from the electrolyte takes place [156].…”

Electrodeposited Gold Nanodaggers on Conductive Metal Oxide Films Provide Substrates for Dual-Modality Surface Sensitive Vibrational Spectroscopy

“…Although the optical response of the metallic films in ATR-SEIRAS is often modeled using effective medium theories − that do not explicitly invoke LSPPs, such substrates should, in principle, also be capable of supporting SERS. However, with the notable exception of Delgado et al’s work, − there have been very few demonstrations of SERS/ATR-SEIRAS complementarity.…”

Spectroelectrochemical and DFT Study of Thiourea Adsorption on Gold Electrodes in Acid Media

“…Spectroelectrochemical studies similar to that reported in this article on the adsorption behavior of simple molecules have been published by our group recently. Namely, the adsorption and reactivity on Au thin-film and single crystal electrodes of some simple amino acids − and a number of acetic acid derivatives − have been studied by combining electrochemical measurements and in situ vibrational spectroscopies. In situ SERS and infrared spectroscopy (either using surface-enhanced infrared reflection–absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) or external reflection configurations) provided molecular level information on the bonding of these adsorbed molecules and on their interactions with coadsorbed water and anions. − This experimental spectroelectrochemical approach, that combines the use of single-crystal electrode surfaces (external reflection experiments) and gold thin film electrodes (ATR-SEIRAS and SERS) has been complemented with the use of DFT to calculate theoretical vibrational spectra from which the observed experimental bands have been assigned.…”