In Situ Stark Effects with Inverted Bipolar Peaks for Adsorbed CO on Pt Electrodes in 50 °C Direct Methanol Fuel Cells

Abstract

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.

Vibrational Spectroscopy for the Characterization of PEM Fuel Cell Membrane Materials

“…In addition, studies that provide more detailed knowledge of vibrational mode assignments, such as those that combine computational methods and spectral measurements on model compounds [51], should continue, as they enable greater understanding to be derived from infrared spectra in relation to structure and function in PEM materials. Further use and development of in situ infrared methods for probing membrane-catalyst interactions in operating fuel cells [23,32,33] and on electrodes [21,22] would also be valuable.…”

“…Compared to in situ diffuse reflectance infrared sampling [23,32,33], Raman measurements can be less invasive. To develop the full potential of Raman spectroscopy for the study of fuel cell membrane materials, there is a need for greater access to instruments with sources that effectively reduce background fluorescence.…”

“…Smotkin and coworkers pioneered an approach for obtaining infrared spectra from membrane electrode assemblies (MEAs) in operating fuel cells [23,32,33]. A thermostatted single fuel cell was modified to accommodate an infrared transparent window ( Fig.…”

“…Diffuse reflectance optics are used to collect radiation emitted from the MEA. The researchers have used the cell mainly to investigate reactions over Pt and Pt alloy anode catalysts during direct methanol fuel cell operation [23,[32][33][34][35]. While studies have focused on the observation of spectral bands arising from methanol oxidation byproducts, the system also provides a means to probe the membrane-catalyst-gas three-phase boundary [34].…”

Operando X‐Ray Absorption Spectroscopy of Polymer Electrolyte Fuel Cells

“…For example, the outer layers of a five-layer membrane electrode assembly consist of carbon gas diffusion layers. A window the size of the IR-beam footprint must be cut out of the gas diffusion layer to expose the catalytic layer [7,[38][39][40][41]. Fan introduced operando FTIR spectroscopy of fuel cells [42][43][44][45] using a diffuse IR fuel cell [45] inserted into a 1990s model Harrick Praying Mantis (Pleasantville, NY) diffuse IR accessory.…”