Surface electrochemistry of CO and H{sub 2}/CO mixtures at Pt(100) interface: Electrode kinetics and interfacial structures
The Pt(100)-CO interaction in aqueous electrolytes was examined by using rotating disk methods in combination with in-situ surface X-ray scattering (SXS) measurements. The analysis of the SXS results indicates that the topmost platinum atoms expand away from the second layer by ca. 4% when H{sub upd} was completely displaced from Pt(100) by CO to form a saturated layer of CO. Assuming that gas-phase heats of adsorption for CO apply as well to the liquid-solid interface, the authors estimate that the Gibbs energy change for the displacement of H{sub upd} by CO on Pt(100) is close to {minus}90 kJ/mol. A Pt(100)-CO surface normal interlayer spacing of 1.4 {+-} 0.4 {angstrom} was extracted from SXS measurements, suggesting that CO is adsorbed primarily at the 2-fold bridge-bonded sites, or possibly a mixture of bridge and atop sites. In contrast to the Pt(111)-CO system, no structures of CO{sub ad} with long-range order were formed on Pt(100). Two different forms of CO{sub ad} are formed at the Pt(100)-electrolyte interface: the weakly adsorbed state which is oxidized in the pre-ignition potential region, and the strongly adsorbed state which is oxidized in the ignition potential region. Although the nature of CO{sub ad} is different before and after the ignition potential, the authors proposed that the mechanism for CO oxidation on Pt(100) is the same in both the pre-ignition and ignition potential regions, e.g., adsorbed CO reacts with hydroxyl species (OH{sub ad}) through a Langmuir-Hinshelwood type reaction. The kinetics of CO oxidation on Pt(hkl) surfaces is found to vary with crystal face. The difference in activity is attributed to the structure-sensitive adsorption of CO, OH{sub ad}, and anions from the supporting electrolytes.
- Research Organization:
- Lawrence Berkeley National Lab., CA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 20003202
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 44; Other Information: PBD: 4 Nov 1999
- Country of Publication:
- United States
- Language:
- English
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