Electrochimica Acta 50 (2005) 2415–2422 Electrooxidation of ethanol on a Pt electrode in acid solutions: in situ ATR-SEIRAS study M.H. Shao, R.R. Adzic ∗ Department of Materials Science, Brookhaven National Laboratory, Upton, NY 11973, USA Received 14 September 2004; received in revised form 12 October 2004; accepted 12 October 2004 Available online 21 November 2004 Abstract The electrooxidation of ethanol was investigated on a Pt thin film electrode in a HClO 4 solution using surface enhanced infrared absorption spectroscopy (SEIRAS) with the attenuated total reflection (ATR) technique. The spectra indicate that during this reaction acetate and CO adsorbates are formed. The intensity of symmetric OCO stretching band of adsorbed acetate correlates well with voltammetry in the potential range between -0.1 and 0.85V. The C=O stretching band for adsorbed acetaldehyde and/or acetyl also was observed; these compounds are the reaction intermediates whose oxidation generates CO ad and acetic acid. We also explored the oxidation behavior of adsorbed residues. The oxidation of acetaldehyde was studied for comparison. © 2004 Elsevier Ltd. All rights reserved. Keywords: Ethanol; Acetaldehyde; Acetic acid; Electrooxidation; Surface enhanced infrared absorption spectroscopy; Platinum 1. Introduction Ethanol is a promising substitute for methanol as fuel in direct alcohol fuel cells (DAFCs) due to its higher en- ergy density and non-toxic properties [1]. The electrooxida- tion of ethanol on platinum electrodes was investigated by several spectroscopic methods, such as infrared reflection- absorption spectroscopy (IRRAS) [2–13], on-line differential electrochemical mass spectrometry (DEMS) [8,10,13–15], and other techniques [13,16–18]. There is a number of ad- sorbed species resulting from the oxidation of ethanol on a Pt surface in acid solution [6,8,12,13,15]. Almost all re- searchers agree that carbon dioxide, acetaldehyde, and acetic acid are the main products of the oxidation of ethanol in acid solution. Carbon dioxide and acetaldehyde were de- tected by DEMS, while acetic acid could not be detected directly by this method because of its very low volatility. All three products were detected by in situ FT-IR. Shin et al. [11] noted adsorbed acetic acid on Pt(1 1 1) and Pt(3 3 5) ∗ Corresponding author. Tel.: +1 631 344 4522; fax: +1 631 344 5815. E-mail address: adzic@bnl.gov (R.R. Adzic). electrodes during ethanol oxidation in acid solution. Iwa- sita and coworkers observed a weak band around 1402 cm -1 and assigned it to adsorbed acetate [9]. A common adsor- bate, CO, is formed from the dissociation of C C bonds at low potentials, as seen in spectroscopic studies. From their FT-IR results, Iwasita and Pastor [8] proposed that the species Pt OCH 2 CH 3 , (Pt) 2 =COH CH 3 , and Pt COCH 3 were the possible adsorbed C2 residues of ethanol adsorp- tion. Surface enhanced infrared absorption spectroscopy (SEIRAS) with attenuated total reflection (ATR) is a promis- ing technique for studying solid–liquid interfaces. By opti- mizing the thickness of the thin film electrode, interference from the solution is minimized leaving only the vibration sig- nals from the adsorbed species. Recently, Osawa and cowork- ers [19–21] described useful findings on the oxidation of methanol and other simple organic molecules using ATR- SEIRAS. In this article, we discuss results from the study of the electrooxidation of ethanol on a Pt thin film electrode by in situ ATR-SEIRAS that describes the behaviors of adsorbed acetate ions and acetaldehyde/acetyl resulting from the reac- 0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2004.10.063