Standard Article

New CO-tolerant catalyst concepts

Electrocatalysis

The hydrogen oxidation/evolution reaction

  1. M. Watanabe

Published Online: 15 DEC 2010

DOI: 10.1002/9780470974001.f204031

Handbook of Fuel Cells

Handbook of Fuel Cells

How to Cite

Watanabe, M. 2010. New CO-tolerant catalyst concepts. Handbook of Fuel Cells. .

Author Information

  1. Yamanashi University, Clean Energy Research Center, Kofu, Japan

Publication History

  1. Published Online: 15 DEC 2010

Abstract

Electrocatalytic activity for H2 oxidation in the presence of 100 ppm CO has been investigated on a series of binary Pt alloy electrocatalysts with nonprecious metals of various compositions, prepared easily by the sputtering method. Regardless of the composition, Pt/Fe, Pt/Ni, Pt/Co and Pt/Mo alloys have been found to exhibit excellent CO tolerance at H2 oxidation similar to Pt/Ru alloy. At these CO tolerant electrodes, the equilibrium coverage of CO was suppressed to values of less than ca. 0.6. Based on X-ray photoelectron spectroscopy, electrochemical quartz crystal microbalance and scanning tunneling microscopy data, it was found that the surfaces of all nonprecious metal alloys are composed of a thin Pt layer with an electronic structure different from that of pure Pt, indicating a modification of the electronic structure by the underlying alloys. It was found that all such CO tolerant alloys exhibit a positive chemical shift in the core-level 4f or 4 d orbitals of Pt and vice versa. Such a modification, indicating 5 d vacancy, can be maintained until the thickness grows up to ca 2 nm, then decreases linearly with the increase of thickness and finally coincides with that of bulky Pt beyond ca. 4 nm. The lowered CO coverage, particularly of multi-bonding, was explained as the result of a lowered 5 d-electron donation from the Pt band to 2π orbital of CO. A weakening of bond strength between the Pt skin layer and CO was also indicated by in situ Fourier transform infrared spectroscopy, suggesting that H2 oxidation sites are not blocked by CO due to its enhanced mobility. Thus, the mechanism of CO tolerance described above at the Pt skin on alloy surfaces is proposed as “detoxification mechanism”. The importance of the examination on the stability as well as the activity of the alloy combinations in the form highly-dispersed on carbon-black supports is pronounced from the viewpoint of the practical application to polymer electrolyte fuel cells.

Keywords:

  • CO tolerant catalyst;
  • CO coverage;
  • polymer electrolyte fuel cells;
  • direct methanol fuel cells;
  • Pt alloy catalyst;
  • Pt/Fe alloy;
  • electrocatalyst design;
  • Fermi level;
  • d-vacancy;
  • sputter deposition;
  • bifunctional mechanism;
  • corrosion resistance;
  • detoxification mechanism