The breaking of the CC bond in ethylene glycol oxidation at the Pt(111) electrode and its vicinal surfaces

Abstract

Please cite this article as: Rosa M. Arán-Ais, Enrique Herrero, Juan M. Feliu, The breaking of the C-C bond in ethylene glycol oxidation at the Pt(111) electrode and its vicinal surfaces, Electrochemistry Communications (2014Communications ( ), doi: 10.1016Communications ( /j.elecom.2014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTThe breaking of the C-C bond in ethylene glycol oxidation at the Pt (111) AbstractEthylene glycol (EG) oxidation has been studied on Pt(111) and its vicinal surfaces in acidic media by cyclic voltammetry and infrared spectroscopy. Even at Pt(111) the C-C bond is readily broken and CO is formed at low potentials. Both types of steps catalyze the EG oxidation to CO 2 , being the {110} steps the most catalytic for the splitting of the C-C bond. Spectroscopic results show that glycolic acid and oxalic acid are produced mainly at the close-packed terraces.

Thermodynamic studies of anion adsorption at the Pt(111) electrode surface from glycolic acid solutions

“…When the cleavage takes place, the fragment containing the carboxylic group will evolve immediately to yield CO 2 . The presence of CO 2 only above 0.5 V suggest that the cleavage is only occurring above this potential, unlike ethanol or ethylene glycol oxidation, where the cleavage occurs at low potentials [7,24,25]. The fragment with the alcoholic group will require and additional O group to yield CO 2 and probably evolves through the formation of CO, as observed for ethanol [24].…”

“…The presence of this latter molecule could be corroborated by the band at 1635 cm -1 , corresponding to the ν as (OCO) mode of bioxalate observed at 0.7 V. In the spectra obtained, the water hides any band present in this region. Nevertheless, in a previous work [7] it was demonstrated the formation of oxalic acid from the oxidation of the alcohol group of the glycolic acid molecule. (iii) The band at 1398 cm -1 is assigned to adsorbed glycolate [22,23], and is present in all the spectra taken between 0.3 V and 0.95 V, clearly related to the adsorption of the anion, discussed in previous paragraphs.…”

“…Over the past year, there has been an increasing interest of these reactions on acidic media because of their potential application on direct alcohol fuel cells using an acidic polymer electrolyte membrane. Among the platinum single crystal electrodes used, Pt(111) seems to be the most reluctant to produce CO 2 in the direct oxidation of ethanol and ethylene glycol, being acetic acid and glycolic acid (GA) almost the only final products, respectively [6,7]. These latter products show voltammetric profiles characteristic of anion adsorption/desorption processes, since their oxidation on platinum only takes place at significant rates at very high potentials.…”

Weakening the C C bond: On the behavior of glyoxylic acid on Pt(111) and its vicinal surfaces

“…In the case of ethanol (EtOH) oxidation reaction (EOR), acetic acid formation through the 4e path predominates against the most desirable 12e path leading to CO 2 as final product. The later route can be favored by weakening the C-C bond by placing electron abstractor groups in the molecule, as has been previously demonstrated for ethylene glycol 4 . In the same way, glycolic acid can be oxidized at platinum (Pt) electrodes at low temperature and concentrations 5 , in contrast to the aforementioned acetic acid.…”

“…It has been previously reported the effect of steps sites in breaking the C-C bond of ethanol and ethylene glycol molecules 4,28,29 . Figure 2 shows the GA oxidation on platinum surfaces with natom wide (111) terrace orientation separated by monoatomic steps with {100} or {110} symmetry.As can be seen in figure 2A, the voltammetric profile does not substantially change from Pt(111) after the insertion of {100} steps (n>9);the current density of both oxidation peaks decreases as the step density increases, being both signals almost negligible for the surfaces with narrow (111) terraces (n<6).…”