DME Dissociation Reaction on Platinum Electrode Surface: A Quantitative Kinetic Analysis by In Situ IR Spectroscopy

Abstract

The kinetics of electrocatalytic dissociation reaction of dimethyl ether ͑DME͒ on a platinum ͑Pt͒ polycrystalline electrode in an acidic solution yielding carbon monoxide ͑CO͒ has been quantitatively analyzed by in situ IR spectroscopy in the potential region between 100 and 500 mV ͑vs reversible hydrogen electrode͒. A two-step consecutive reaction model, an initial dehydrogenation step followed by a CO formation step, is proposed for the dissociation process of the DME molecule. The mechanism of the DME dissociation on the Pt electrode surface is discussed based on the kinetic analysis. Dimethyl ether ͑DME, CH 3 OCH 3 ͒ is considered a promising fuel in direct fuel cells 1-6 because of several advantages over methanol and other small organic molecules: higher energy density, lower toxicity, and lower crossover to the cathode.

Electrochemical behaviors of dimethyl ether on platinum single crystal electrodes. Part II: Pt(100)

“…No peak is observed in the IR spectra when the electrode potential is lower than 0.20 V, indicating that the decomposition of DME molecule does not occur as the hydrogen coverage is high as that reported previously on Pt(1 1 1) [11,12] and Pt(poly) electrodes [ 13,14]. Four small upward IR peaks are observed around 1320, 1480, 1822 and 2016 cm À1 at 0.3 V, indicating that some surface species are formed from the potential.…”

“…The Peaks I and II were almost the same by keeping E ad at 0.05 V for different time, suggesting that DME decomposition reaction hardly occurs at 0.05 V where Pt(1 0 0) electrode surface is fully covered by hydrogen [13,14] but will take place at a more positive potential where some surface sites are released from hydrogen desorption. Fig.…”

“…Such problem can be avoided using the surface enhanced IR measurement with the Kretschmann attenuated total reflection (ATR) configuration while the electrode is only limited to polycrystalline thin-film metal electrodes [13,14]. At the present stage, the thin-layer geometry is the only possible design for in situ IR measurement on the single crystal electrode surface and several improvements have been proposed by introducing the forced mass transport in the thin-layer [28][29][30].…”

“…Many works have been carried out on DME concerning its electrooxidation behaviors [4][5][6][7] and development of the novel electrocatalysts [8][9][10]. Recently, we studied the electro-oxidation behaviors of DME on platinum single crystal Pt(hkl) and polycrystalline Pt(poly) electrode surfaces by cyclic voltammograms (CVs) and in situ time-resolved infrared (IR) spectroscopy [11][12][13][14]. It is found that DME electro-oxidation behaviors significantly depend on the surface structure of Pt(hkl) electrodes.…”

“…Although these measurements were carried out in acidic solutions under similar conditions, most of the in situ IR characterization results are quite different. Recently, the electro-oxidation reactions of the DME on Pt(poly) electrode have been carefully investigated by electrochemical and in situ IR measurements in our group after several improvements in experimental conditions used in previous works [13,14]. Our observations show that a reaction intermediate species, (CH 3 OCH 2 -) ad , is generated in the hydrogen adsorption potential region as an initial product for dehydrogenation process of DME and is subsequently decomposed to adsorbed carbon monoxide (CO ad ) and finally oxidized to CO 2 in positive potential region [13,14].…”