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Mechanistic aspects of carbon monoxide oxidation

Advances in Electrocatalysis, Materials, Diagnostics and Durability

Electrocatalyst materials for low temperature fuel cells

Fundamental catalysis models

  1. T. Iwasita,
  2. E. G. Ciapina

Published Online: 15 DEC 2010

DOI: 10.1002/9780470974001.f500014

Handbook of Fuel Cells

Handbook of Fuel Cells

How to Cite

Iwasita, T. and Ciapina, E. G. 2010. Mechanistic aspects of carbon monoxide oxidation. Handbook of Fuel Cells. .

Author Information

  1. Universidade de São Paulo, IQSC, Sao Carlos, Brazil

Publication History

  1. Published Online: 15 DEC 2010

Abstract

Some experimental and theoretical approaches to formulating a reaction mechanism for carbon monoxide (CO) oxidation at Pt-based catalysts are discussed. According to these, it is likely that the reaction takes place at steps and defect sites on the surface, thus called active sites. On these sites, dissociation of water occurs and CO from the terraces diffuses to the active sites, where a Langmuir–Hinshelwood mechanism between COad and OHad takes place. Potentiostatic and potentiodynamic data for CO stripping at nanoparticles show that the oxidation occurs with a higher rate at large nanoparticles following the same reaction mechanism as for extended surfaces with a high rate of CO diffusion. In contrast, at small particles (∼1 nm) CO diffusion is rate determining. It is shown that an L–H mechanism is also operative in the presence of dissolved CO, in spite of the high degree of CO surface coverage. Under the latter conditions, large currents are observed in the prepeak region if CO is preadsorbed at potentials below the potential of zero charge (pzc) (∼0.30 vs standard hydrogen electrode — SHE). CO preadsorption above this potential causes an inhibition of CO oxidation. This inhibition is likely due to the formation of icelike water clusters, mainly at the steps. This interpretation is based on Fourier transform infrared spectroscopy (FTIRS) and scanning tunneling microscopy (STM) data. Adsorbed anions have an inhibiting effect on both monolayer and bulk CO oxidation. The enhancement of CO oxidation by PtRu and PtSn is discussed in the light of recently developed theories on bimetallic catalysts.

Keywords:

  • carbon monoxide;
  • CO oxidation mechanism;
  • CO oxidation inhibition;
  • icelike water clusters;
  • active sites