In Situ Infrared Spectroscopy
Reviews:
C. Korzeniewski, “Infrared Spectroelectrochemistry” In Handbook of Vibrational Spectroscopy, J.M. Chalmers and P.R. Griffiths, Eds., Wiley: New York, Volume 4, (2002) pp. 2699 - 2710.
Korzeniewski, C. “Vibrational Coupling Effects on Infrared Spectra of Adsorbates on Electrodes” In Interfacial Electrochemistry, Wieckowski, A., Ed., Marcel Dekker, Inc.: New York, 1999, pg. 345-352.
Korzeniewski, C. “Infrared spectroscopy in electrochemistry: New methods and the connection to UHV surface science" Critical Reviews in Analytical Chemistry 27 (1997) 81-102.
Projects:
1. Probing CO adsorption at different structural sites on stepped single crystal electrode surfaces.
Early research in the group focused on the study of adsorption at stable high index surface planes of single crystal electrodes. The step sites on the surfaces serve as models of the edges and defects on practical catalysts. These low coordination sites can be the most active.
Infrared spectra of CO adsorbed at stepped surface planes of single crystals show effects of vibrational coupling. On platinum, CO bonding is most energetically favorable at steps. When the coverage is low, vibrational bands can be assigned to CO bound to step sites. As the steps fill and terraces become populated, infrared bands arise from modes that involve the coupled vibrational motion of molecules at the different types of sites. The dependence of band positions and intensities on CO surface coverage can be correlated to the strength of intermolecular forces between adsorbed molecules. We have used these relationships to obtain information about adlayer structures formed by CO adsorbed on stepped Pt single crystal electrodes.
The Figure at the left shows spectral bands associated with vibrational modes of CO at step and terrace sites of Pt(557). Additional information can be found in the following references:
Kim, C.S.; Korzeniewski, C. “Vibrational coupling as a probe of adsorption at different structural sites on a stepped single crystal electrode” Anal. Chem. 69 (1997) 2349-2353.
Shin, J.; C. Korzeniewski "Infrared spectroscopic detection of CO formed at step and terrace sites on a corrugated electrode surface plane during methanol oxidation" J. Phys. Chem. 99 (1995) 3419-3422.
Kim, C.S.; Tornquist, W.J.; Korzeniewski, C. "Site-dependent vibrational coupling of CO adsorbates on well-defined step and terrace sites of monocrystalline platinum: Mixed-isotope studies at Pt(335) and Pt(111) in the aqueous electrochemical environment" J. Chem. Phys. 101 (1994) 9113-9121.
2. In situ infrared measurements at above ambient temperatures.
Fundamental investigations of CO electrochemistry are motivated in large part by the role of CO as a catalyst poison in polymer electrolyte membrane (PEM) fuel cells that operate on reformed H2 and as a reaction intermediate and potential poison in direct methanol fuel cells. Since these fuel cells operate at above ambient temperatures, at least up to about 100 °C, it is desirable to probe the surface electrochemistry of CO and related species at the same temperatures. To facilitate such studies, we have constructed a temperature controlled infrared spectroelectrochemical cell. The cell design and some of its applications are reported in the references below. The figure shows in situ IR spectra that demonstrate the thermal activation of methanol dissociative chemisorption on a high Ru content bulk Pt-Ru alloy.
D. Kardash, C. Korzeniewski, N. Markovic “Effects of Thermal Activation on the Oxidation Pathways of Methanol at Pt-Ru Alloy Electrodes” J. Electroanal. Chem. 500 (2001) 518-523.
D. Kardash, C. Korzeniewski, “Temperature Effects on Methanol Dissociative Chemisorption and Water Activation at Polycrystalline Platinum Electrodes” Langmuir 16 (2000) 8419-8425.
D. Kardash, J. Huang, C. Korzeniewski, “A Jacketed Cell for Infrared Spectroelectrochemistry at Constant Above Ambient Temperatures” J. Electroanal. Chem. 476 (1999) 95-100.
3. In situ infrared measurements at carbon supported fuel cell catalysts.
Catalysts employed in PEM fuel cells are typically Pt crystallites that have diameters of a few nanometers (ca. 1-3 nm) supported on carbon. In situ IR studies of reactions at the supported catalysts are made difficult by the low reflectivity of the carbon. To overcome this limitation, we have been using a procedure that enables Vulcan carbon supported transition metal catalysts to be adsorbed as a thin layer on gold. The high reflectivity of the gold allows catalyst surface chemistry to be probed in situ with IR spectroscopy. The approach was developed by the Weaver group at Purdue University: S. Park, S.A. Wasileski and M.J. Weaver J. Phys. Chem B 105, 9719 (2001).
We have been investigating the surface chemistry of CO, formic acid and methanol on Vulcan carbon supported Pt and Pt-Ru catalysts that have low metal loadings (below 15%). Effects of temperature, reactant concentration, catalyst properties and electrode potential on reaction pathways are under study. For example, the figure at the left displays in situ IR spectra recorded during formic acid oxidation on a low metal loading (10%) Vulcan carbon supported Pt catalyst. The bands at 2277 cm-1 arise from 13CO2. The spectra demonstrate the early onset of CO2 formation at 0.2 V.