Environmental Engineering Reference
In-Depth Information
&
CHAPTER 6
Mechanisms of the Oxidation of
Carbon Monoxide and Small Organic
Molecules at Metal Electrodes
MARC T.M. KOPER and STANLEY C.S. LAI
Leiden Institute of Chemistry, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands
ENRIQUE HERRERO
Instituto de Electroquimica, Universidad de Alicante, Apartado 99, E-03080, Alicante, Spain
6.1 INTRODUCTION
The electrochemical oxidation of carbon monoxide (CO) and small organic molecules
containing one or two carbon atoms is one of the central catalytic issues in the success-
ful development of low temperature fuel cells. Methanol and ethanol are the most
likely candidates for direct alcohol fuel cells, but the significant overpotential for
their oxidation severely limits the fuel cell's efficiency. Understanding the nature of
this overpotential is key to the development of better fuel cell catalysts, and also
involves understanding the reactivity of intermediates in methanol and ethanol
oxidation. CO is the most prominent intermediate, the oxidation of which is also of
great significance for hydrogen - oxygen fuel cells in which the hydrogen stream is
contaminated by small traces of CO.
This chapter summarizes our current understanding of the mechanisms of the
oxidation of CO, methanol, and ethanol, as well as the important organic intermediates
formaldehyde and formic acid, as gleaned from surface science-type studies employ-
ing well-defined monometallic electrode surfaces ( primarily single crystals) combined
with in situ spectroscopy and kinetic modeling. Computational methods such as
density functional theory (DFT) are also beginning to contribute importantly to the
unraveling of kinetic and thermodynamic factors, reaction pathways, and structure
sensitivity issues in electrocatalysis research, and relevant results will be cited
where appropriate. In the concluding section, we will also touch upon the relation
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