Environmental Engineering Reference
In-Depth Information
& CHAPTER 14
The Effect of Structurally Well-Defined
Pt Modification on the Electrochemical
and Electrocatalytic Properties of
Ru(0001) Electrodes
H.E. HOSTER and R.J. BEHM
Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany
This chapter is dedicated to Professor Teresa Iwasita on the occasion of her 65th
birthday and in recognition of her contributions to electrocatalysis
14.1 INTRODUCTION
Carbon-supported PtRu catalysts have become the state-of-the-art anode catalysts in
polymer electrolyte fuel cells (PEFCs) operated by CO-containing fuel gases [Petry
et al., 1965] resulting, for example, from steam reforming of hydrocarbons or alcohols
[Peppley et al., 2003], and in direct methanol fuel cells (DMFCs) [Hamnett, 2003]. Their
higher CO tolerance and activity with respect to methanol oxidation compared with Pt
catalysts has been attributed to a bifunctional effect, where facile formation of adsorbed
oxygen species on Ru sites and their reaction with CO ad adsorbed on neighboring Pt
sites results in a reduction of the steady-state CO ad coverage at significantly lower poten-
tials than on Pt, and hence in improved CO tolerance [Watanabe and Motoo, 1975;
Gasteiger et al., 1994a]. More recently, a reduced CO adsorption energy, and hence
an increased tendency for CO ad desorption, was proposed as a second effect contributing
to the higher CO tolerance of these bimetallic catalysts [Buatier de Mongeot et al., 1998;
Koper, 2004; Diemant et al., 2003; Liu et al., 2003]. The mechanistic aspects underlying
the improved CO tolerance and methanol oxidation activity of PtRu catalysts have been
investigated in a number of experimental and theoretical studies on bimetallic
PtRu model systems [Gasteiger et al., 1994a, b; Binder et al., 1972; Stimming and
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