| Abstract
| - Submonolayer amounts of Ru have been deposited on a polycrystalline Pt bead electrode from a solutioncontaining 6.68 × 10-4 mol dm-3 RuNO(NO3)3 using an impinging jet apparatus. Deposition of Ru on aplatinum surface almost completely covered with Hads due to exchange of the adsorbed hydrogen with Ru3+produces a surface coverage of 0.12 ± 0.02. The reduction of Ru occurs via two separate pathways: in one,metallic Ru is deposited on the surface; in the other, the complex is reduced to an intermediate oxidationstate and remains soluble. The latter process, which occurs at potentials less than about 0.25 V has not beenpreviously reported and may explain some of the discrepancies seen in the literature. For characterization ofthe resultant Pt(Ru) surface we compare the approach developed by Motoo and Watanabe (J. Electroanal.Chem. 1975, 60, 267−273) and Frelink et al. (Langmuir1996, 12, 3702) with that utilizing copper upd.The latter approach is applicable for Ru coverage from 0 up to at least 0.80, whereas the former methods areonly applicable up to a coverage of ca. 0.30. On addition of Ru to a clean Pt surface a small initial drop intotal surface area is seen, but the area then remains quite constant with increasing Ru coverage. In comparison,the charge measured from stripping of a saturated CO layer adsorbed at 0.3 V(RHE) shows an increase withRu coverage. The most active surface for the oxidation of an adsorbed CO layer as measured by the potentialat which half of the CO has been oxidized is found to contain a Ru surface coverage of 0.2. In comparison,for the oxidation of methanol at 25 °C, it is found that there is a broad maximum in catalytic activity for Rusurface coverage in the range 0.25−0.5. The long term poisoning rate of the electrodes is highly dependentupon Ru coverage, showing a minimum over the range 0.4−0.6.
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