Electrochimica Acta 51 (2005) 1085–1090 Electro-oxidation of methanol and ethylene glycol on platinum in alkaline solution: Poisoning effects and product analysis Koji Matsuoka a , Yasutoshi Iriyama a , Takeshi Abe a , Masao Matsuoka b , Zempachi Ogumi a,∗ a Department of Energy & Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan b Faculty of Science & Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan Received 25 January 2005; received in revised form 27 May 2005; accepted 6 June 2005 Available online 18 July 2005 Abstract The electrochemical oxidation of ethylene glycol on platinum was investigated and compared with that of methanol in alkaline solution by using various electrochemical and analytical measurements. Ethylene glycol showed much less significant electrode poisoning than methanol at low potential (400 mV). This phenomenon was clarified by analyzing the products of ethylene glycol oxidation. In ethylene glycol oxidation, partial oxidation to glycolate was much faster than complete oxidation to CO 2 . In addition, there were two paths for ethylene glycol oxidation: poisoning and non-poisoning paths. The poisoning path led to the production of C1 compounds and the non-poisoning path gave oxalate. The non-poisoning path prevented the formation of poisonous species on platinum. © 2005 Elsevier Ltd. All rights reserved. Keywords: Fuel cell; Electro-oxidation; Methanol; Ethylene glycol; Poisoning; Alkaline solution; Reaction mechanism; Product analysis 1. Introduction Direct alcohol fuel cells (DAFCs) have recently received considerable attention. DAFCs can be made quite compact without a bulky external reformer, which is essential for polymer electrolyte membrane fuel cells (PEMFC) which use hydrogen gas. Therefore, DAFCs can be used as power sources in portable electronic devices, such as cellular phones and laptop computers. Liquid fuels, such as small molec- ular weight alcohols, which have higher volumetric energy density and better energy efficiency, are easier to store and transport than gaseous fuels. Direct methanol fuel cells (DMFCs) have been widely investigated [1–3]. However, the further development of DMFCs faces some serious difficulties [4,5] before they can be put touse: (i) slow electrode-kinetics of methanol oxidation and (ii) CO poisoning of the Pt electrode at low temperature. In addition, the high volatility and toxicity of methanol may ∗ Corresponding author. E-mail address: ogumi@scl.kyoto-u.ac.jp (Z. Ogumi). cause serious problems when portable electronic devices with DMFCs as power sources are commercialized, though these problems are currently underestimated. Recently, we reported the anodic oxidation of polyhydric alcohols on a platinum electrode in alkaline solution [6]. Polyhydric alcohols, such as ethylene glycol and glycerol, are much less volatile and less toxic than methanol. These polyhydric alcohols can be electrochemically oxidized and ethylene glycol shows higher reactivity than methanol and other polyhydric alcohols in alkaline solutions. The peak cur- rent densities in cyclic voltammograms for ethylene glycol were 6 and 1.5 times as large as those for methanol in KOH and K 2 CO 3 solution, respectively [6]. In general, the problem with alkaline fuel cells is pro- gressive carbonation of the solution caused by CO 2 in air or produced by oxidation reactions. Thus, due to the dissolu- tion of carbon dioxide, the pH value of the alkaline solution decreases, leading to a decrease in reactivity according to the reaction: CO 2 + 2OH - → CO 3 2- + H 2 O 0013-4686/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2005.06.002