The Potential Dependence of Intermediates in Methanol Oxidation Observed in the Steady State by FTIR Spectroscopy

Abstract

The structure of electrochemical intermediates of methanol oxidation on platinum in aqueous sulfuric acid has been investigated under steady state conditions using polarization modulation Fourier transform infrared reflection absorption spectroscopy. Terminally bonded CO and bridge‐bonded CO are observed in the cathodic to anodic sequence. However, only bridge‐bonded CO is observed in the anodic to cathodic sequence. The conventionally assumed C‒O‒H group was not observed. The spectroscopic results are compared with similar information obtained by means of radiotracer and potentiodynamic techniques. A new mechanism is proposed which is intended to apply to the steady‐state situation and may differ from that pertaining to potential sweep data.

DMFCs: From Fundamental Aspects to Technology Development

“…The mechanism by which such synergistic promotion of the methanol oxidation reaction is brought about has been the subject of numerous studies during the last 30 to 40 years, in which various spectroscopic methods have been employed in conjunction with electrochemistry [4±8]. A combination of cyclic voltammetry [18], in-situ ellipsometry [33], Xray absorption spectroscopy [31], on-line mass spectrometry [30] and in-situ FTIR spectroscopic studies [22,28,29], revealed that the electro-oxidation of methanol on Pt-based catalysts proceeds through the mechanism (sequence of non-elementary reaction steps) described below. First a sequence of dehydrogenation steps give rise to adsorbed methanolic residues, according to the following scheme:…”

“…PtOH + Pt CO À3 2Pt + CO 2 + H + + 1e ± (13) The overall oxidation process of methanol to carbon dioxide proceeds through a six electron donation process; yet, the rate determining step, derived from electrochemical steadystate measurements on Pt, through the analysis of the Tafel slope, involves a one-electron step [22]. On a pure Pt surface, the dissociative chemisorption of water on Pt is the rate determining step at potentials below % 0.7 V vs. RHE, i.e.…”

Direct Methanol Fuel Cells: History, Status and Perspectives

“…However, an in-depth analysis of the methanol oxidation process, initially at smooth electrode surfaces, was made possible by the use of spectro-electrochemical methods. This work was carried out by several groups including those of Lamy [35], Bockris [36] and Christensen [37]. These studies essentially investigated adsorbed methanolic residues by infrared spectroscopy whereas, for the adsorbed oxygen species, ellipsometry gave appropriate results [38].…”

Application of photothermal deflection spectroscopy to electrochemical interfaces

“…But the failure of Raman to achieve monolayer sensitivity, and the development of Fourier transform spectrometers led to a renewed interest in simple reflection spectroscopies. In situ IR reflectance has been applied to electrochemical interfaces by Bewick and Pons, and many others [114][115][116][117][118][119][120][121][122][123][124]. 3 In situ reflectance spectroscopy has also been performed in the visible region [125 -128], but more attention has been given to IR spectroscopy, which provides vibrational information.…”