Journal of Power Sources 185 (2008) 853–856 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Preliminary study of ethanol electrooxidation in the presence of sulfate on polycrystalline platinum R.S. Ferreira Jr., V.R. Oliveira, R.G.C.S. Reis, G. Maia, G.A. Camara ∗ Departamento de Química/UFMS, C.P. 549, 79070-900, Campo Grande, MS, Brazil article info Article history: Received 9 June 2008 Received in revised form 15 September 2008 Accepted 19 September 2008 Available online 25 September 2008 Keywords: Electrocatalysis Ethanol electrooxidation Influence of sulfate concentration Sulfate adsorption Polycrystalline platinum abstract The electrooxidation of ethanol and its inhibition by the presence of adsorbed sulfate have been inves- tigated by cyclic voltammetry and chronoamperometry using several concentrations of sulfuric acid on smooth polycrystalline platinum. The results show that the concentration of sulfuric acid influences the current in both potentiostatic and potentiodynamic experiments. The results are interpreted in terms of the competitive adsorption of sulfate and ethanol on the same Pt sites and suggest that, when the sulfuric acid concentration is increased, there is a reduction of Pt free sites able to adsorb and oxidize ethanol. The voltammetric data reveal that the peak currents observed during ethanol oxidation are not affected in the same way by the presence of H 2 SO 4 , which, based on previously obtained FTIR results, suggests that the sulfate adsorption is able to inhibit the oxidation of ethanol in a selective way. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The inhibitory nature of sulfate in the oxidation of organic molecules is well known in the literature [1–4]. Studies on sulfate ions are important because sulfate ions are widely used in sup- porting electrolytes for electrochemical studies. In the early 1980s Sneel and Keenan showed that the current peak values for the three anodic waves of ethanol oxidation in polycrystalline Pt are lower in the presence of H 2 SO 4 than HClO 4 [1]. Due to strong specific adsorp- tion on Pt, sulfate and bisulfate has been widely investigated in the last 20 years on lower-index surfaces of this metal [5–10]. Iwasita et al. investigated the adsorption of sulfate on Pt (1 0 0), (1 1 0) and (1 1 1) [11]. Using FTIR in situ, the authors conclude that sulfate has a tendency to attain the maximum possible coordina- tion. As a consequence, sulfate exhibits triple coordination on Pt (1 1 1) and double coordination on Pt (1 0 0) and Pt (1 1 0). Results obtained from radiochemical measurements show that the maximum coverage of Pt (1 1 1) in 10 -3 MH 2 SO 4 is 2.4 × 10 14 ions cm -2 [12]. A fast calculation shows that about half of the surface is covered by SO 4 2- ions. This relatively high coverage implies that the presence of sulfate can influence the adsorption and oxidation of organic molecules. ∗ Corresponding author. Tel.: +55 67 3345 7012; fax: +55 67 3345 3552. E-mail address: gacamara@nin.ufms.br (G.A. Camara). Similarly, Iwasita et al. have investigated the electrooxidation of methanol in the presence of 0.5 M H 2 SO 4 on smooth polycrys- talline Pt and Pt (1 1 1) [3,4]. Using HPLC and FTIR in situ, the authors show that methanol electrooxidation at Pt (1 1 1) occurs via paral- lel pathways that produce HCHO, HCOOH and CO 2 . Moreover, the authors conclude that the CO 2 pathway is inhibited in the presence of sulfate, while those involving the production of formaldehyde and formic acid are not affected. Despite the interesting findings of Iwasita and co-workers con- cerning methanol oxidation in the presence of H 2 SO 4 [3,4] and the several papers devoted to the study of sulfate adsorption on Pt [13–15], Au [16–20], Pd [21–23], Rh [24] and other metals [25–27], there have, until now, been no further papers on sulfate adsorp- tion in the presence of ethanol after the introductory investigation made by Sneel and Keenan, at least to our knowledge. The electrooxidation of ethanol has been a matter of growing interest in the last few years [28–35], because ethanol can be used in fuel cells, mainly due to its renewable nature and high energetic content [36]. Another important aspect concerning ethanol is the fact that it has the simplest carbon chain of all alcohols (2 atoms). Thus, studies involving ethanol are relevant for the development of catalysts able to break C C bonds. These characteristics have made ethanol oxidation a central point of interest from both fundamental and applied points of view. This paper presents a preliminary study of the catalytic activ- ity of smooth polycrystalline Pt on the electrochemical oxidation of ethanol as a function of the concentration of sulfuric acid. The 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.09.060