Macroporous Ru, Os, Re, RuOs, and RuRe films were deposited on the Pt substrate by a hard template method in which electrodeposition of the oxophilic metal was confined to the interstices formed by annealed closely packed uniform polystyrene spheres self-assembled on the Pt substrate. X-ray diffractometry indicated that co-deposited RuOs and RuRe adopted the ruthenium's hcp (hexagonal close-packed) structure with some negative shifts in the Bragg angles. X-ray photoelectron spectroscopy detected the following major oxidation states on the metal surface: Pt 0 on Pt; Ru 0 on Ru, RuOs, and RuRe; Os 0 on Os and RuOs; and Re VII on Re and RuRe. Both CO stripping voltammetry and chronoamperometric measurements showed that the Pt−RuOs pair sites were most active for sustained CO oxidation, followed by the Pt−RuRe, Pt−Ru, and Pt−Os pair sites, in that order. The trend is explained in terms of the strength of OH adsorption on the oxophilic metals and the contributions of OH ad to the overall methanol oxidation reaction. The use of regular structured porous films on the Pt substrate with distinct Pt−oxophilic metal(s) interfaces removes many of the ambiguities in assigning the observed activity difference to the effects of different Pt−oxophilic metal pair sites.
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Liu et al. (2006) studied this question.
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