Mechanistic Study of Methanol Oxidation over Platinum Electrode in Alkaline Aqueous Solutions

• Published in: Meeting abstracts (Electrochemical Society) Vol. MA2016-02; no. 53; p. 3996
• Main Authors: Kubota, Ryoma, Okanishi, Takeou, Muroyama, Hiroki, Matsui, Toshiaki, Eguchi, Koichi
• Format: Journal Article
• Language: English
• Published: 01.09.2016
• ISSN: 2151-2043; 2151-2035
• DOI: 10.1149/MA2016-02/53/3996

Hydrogen is a clean fuel for stationary, mobile and transportation applications, particularly for fuel cells, but its storage and delivery are still major issues. To overcome these problems, hydrogen has been stored and transported via other chemical compounds, such as alcohols, hydrocarbons, ammonia, etc. Methanol is a promising hydrogen career due to its high volumetric energy density and ease in handling and storage. Direct methanol fuel cells (DMFCs) have been mainly studied with acidic electrolytes and the methanol oxidation mechanism has been clarified to some extent in recent years [1]. However, rare and expensive Pt–based electrocatalysts are normally used in DMFCs. One promising approach to improve this problem is using alkaline electrolytes because of the potential use of non–Pt catalysts. Nevertheless, there are few studies on the methanol oxidation mechanism in alkaline media. In this study, the electrochemical oxidation of methanol over Pt electrode in an alkaline solution was investigated using linear sweep voltammetry and in situ attenuated total reflection infrared (ATR–IR) spectroscopy. 　The oxidation current of methanol was observed at approximately 0.4–0.9 V in 0.25 M KOH–0.25 M CH 3 OH in the linear sweep voltammogram (LSV). In the time–resolved IR spectra acquired simultaneously with the LSV, two characteristic bands ascribable to the adsorbed formic acid species (HCOO ad ) were detected at 1800 cm –1 and 2000 cm –1 in the potential range of 0.1–0.3 V, and their intensity decreased with an increase in potential [2]. Alternatively, the new bands attributable to the aldehyde species (H x CHO ad ) appeared at 0.2 V in the same wavenumber range. These bands shifted to higher wavenumber with a rise in the potential probably due to the dipole–dipole coupling effect [3], and disappeared above 0.8 V. These results clarified that the formic acid species was oxidized in the initial step of methanol oxidation, followed by the aldehyde species. Therefore, aldehyde species and formic acid species were found to be the intermediates of the methanol oxidation. Since the aldehyde species existed over Pt electrode even at higher potential of 0.8 V, the development of the electrocatalysts active for the H x CHO ad oxidation reaction will be required for the enhancement of methanol oxidation in alkaline media. REFERENCES [1] N. M. Markovic, H. A. Gasteiger, P. N. Ross Jr, Electrochim. Acta , 40 (1995) 91–98 [2] G. Samjeske, M. Osawa, Angew. Chem. Int. Ed ., 117 (2005) 5840–5844. [3] Y. Y. Yang, J. Ren, H. X. Zhang, Z.Y. Zhou, S. G. Sun, W. B. Cai, Langmuir , 29 (2013) 1709–1716.