The potential- and coverage-dependent infrared absorption spectroscopy (IRAS) of linearly bound CO on single-phase polycrystalline arc-melted Pt, PtRu(1/1), PtRu(8/2), PtOs(8/2), PtRuOs(8/1/1), PtRuOs(65/25/10), and Ru electrodes in 0.5 M H2SO4 are correlated with the potential-dependent X-ray photoelectron spectroscopy (XPS) of the PtRu(1/1), PtOs(8/2), and PtRuOs(65/25/10) substrates. The CO stretching frequencies decrease as the mole fraction of Pt in the alloy is decreased. The CO oxidation onset on pure Pt at 100.0% CO coverage is 0.5 V vs a reversible hydrogen electrode and shifts negatively as the alloy mole fraction of Pt is reduced. At CO dosing conditions that yield 100% coverage on pure Pt, the CO bandwidths increase with decreasing Pt mole fraction:  on pure Pt the bandwidths increase as the CO coverage is reduced. The effects of CO coverage and bulk alloy composition on the Stark tuning rates (STRs) have been systematically examined on Pt, and a series of binary and ternary alloy surfaces. The XPS data confirm a potential-dependent surface distribution of oxides and no significant surface segregation of the alloying components. The systematic displacement, to lower frequencies, of the linear STRs as the mole fraction of Pt is reduced suggests no significant island formation on the arc-melted alloy surfaces. The XPS data also suggest that the alloying metals, rather than Pt, are responsible for activation of the water required for methanol oxidation in the direct methanol fuel cell potential window.

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A tandem surface-transmission Fourier transform infrared (FTIR) method permits the simultaneous investigation of adsorbed and desorbed species formed at the electrode surface of direct methanol fuel cell (DMFC) membrane electrode assemblies (MEAs). Potential dependent, in situ specular reflectance spectra and on-line transmission FTIR spectroscopy of adsorbed and desorbed species on working fuel cell electrode surfaces, confirm that linear bound CO, the primary intermediate on unsupported Pt and PtRu surfaces of fuel cell MEAs, have lower Stark tuning rates than the corresponding on arc-melted alloys. Two peaks corresponding to CO stretching modes were observed on a PtRu fuel cell anode surface prepared with Johnson Matthey catalysts. The higher frequency peak is ascribed to a Pt-rich alloy and the low frequency peak is ascribed to either pure Ru or an Ru-rich phase. The tandem technique confirms that a peak easily misassigned as a linear bound CO stretching mode false(2083 cm−1false) is a methanol overtone peak. In addition to CO2, methylformate is a major product of a gas fed DMFC, which is detected at the anode exhaust by on-line FTIR. © 2002 The Electrochemical Society. All rights reserved.

Adsorbed CO Stark tuning rates have been studied for the first time in direct methanol fuel cells on Pt black catalysts supported only on the polymer electrolyte (Nafion) in membrane electrode assemblies. The bipolar peaks resulting from the Stark shift of CO absorbance peaks are inverted, indicating an anomalous increase in the reflectivity where CO infrared absorption occurs. The vibrational Stark tuning data suggests that CO oxidation occurs on the perimeter of COads islands, which is consistent with the formation of CO within and above Pt double layer potentials as reported by Kunimatsu. This is expected since methanol is continuously delivered to the anode at all potentials in direct methanol fuel cells.

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