Electro-Oxidation of Ethylene Glycol on a Pt-Film Electrode Studied by Combined in Situ Infrared Spectroscopy and Online Mass Spectrometry

Adsorption and oxidation of ethylene glycol (EG) on a Pt thin film electrode was investigated in a combined spectro-electrochemical approach under continuous flow conditions, including potentiodynamic, potentiostatic, as well as adsorbate-stripping experiments. During the adsorption/electro-oxidation of EG, the potential-dependent development of the EG adlayer was followed by highly surface sensitive, in situ attenuated total reflection Fourier transform infrared spectroscopy, while the volatile products were simultaneously monitored by online differential electrochemical mass spectrometry. For the assignment of the detected IR bands, comparative experiments following the adsorption/oxidation of the possible reaction intermediates/products (glycolaldehyde, glycolic acid, glyoxal, glyoxylic acid oxalic acid) were performed. The data show that (i) during the adsorption/oxidation of EG, CO_ad is formed in the potential range between 0.1 and 0.7 V_RHE, which can be oxidized further to CO₂ at potentials above 0.5 V. (ii) In addition to CO_ad, adsorbed 2-hydroxyacetyl and glycolate were detected, where (iii) 2-hydroxyacetyl is a precursor to form adsorbed CO, and (iv) adsorbed glycolate exists in equilibrium with glycolic acid in solution.