The electrochemical deposition of Ru on Pt(111) electrodes has been investigated by electron diffraction, Auger spectroscopy, and cyclic voltammetry in a closed UHV transfer system. At small coverages Ru formed a monatomic commensurate layer, at higher coverage mostly small islands with a bilayer height were detected. When the Pt was almost completely covered by Ru, three-dimensional clusters developed. The island structure of Ru changed upon electrooxidation of CO, reflecting an enhanced mobility of Ru. Adsorption and electrooxidation of CO have been studied on such Ru-modified Pt(111) electrodes using cyclic voltammetry and in situ FTIR spectroscopy. Compared to the pure metals, the Ru−CO bond is weakened, the Pt−CO bond strengthened on the modified electrodes. The catalytic activity of the Ru/Pt(111) electrode toward CO adlayer oxidation is higher than that of pure Ru and a PtRu alloy (50:50). It is concluded that the electrooxidation of CO takes place preferentially at the Ru islands, while CO adsorbed on Pt migrates to them.

The electrochemical uptake of oxygen on a Ru(0001) electrode was investigated by electron diffraction, Auger spectroscopy, and cyclic voltammetry. An ordered (2 × 2)-O overlayer forms at a potential close to the hydrogen region. At +0.42 and +1.12 V vs Ag/AgCl, a (3 × 1) phase and a (1 × 1)-O phase, respectively, emerge. When the Ru electrode potential is maintained at +1.12 V for 2 min, RuO2 grows epitaxially with its (100) plane parallel to the Ru(0001) surface. In contrast to the RuO2 domains, the non-oxidized regions of the Ru electrode surface are flat. If, however, the electrode potential is increased to +1.98 V for 2 min, the remaining non-oxidized Ru area also becomes rough. These findings are compared with O overlayers and oxides on the Ru(0001) and Ru(101̄0) surfaces created by exposure to gaseous O2 under UHV conditions. On the other hand, gas-phase oxidation of the Ru(101̄0) surface leads to the formation of RuO2 with a (100) orientation. It is concluded that the difference in surface energy between RuO2(110) and RuO2(100) is quite small. RuO2 again grows epitaxially on Ru(0001), but with the (110) face oriented parallel to the Ru(0001) surface. The electrochemical oxidation of the Ru(0001) electrode surface proceeds via a 3-dimensional growth mechanism with a mean cluster size of 1.6 nm, whereas under UHV conditions, a 2-dimensional oxide film (1−2 nm thick) is epitaxially formed with an average domain size of 20 μm.

In situ FTIR spectroscopic and electrochemical data and ex situ (emersion) electron diffraction (LEED and RHEED) and Auger spectroscopic data are presented on the structure and reactivity, with respect to the electro-oxidation of CO, of the Ru(0001) single-crystal surface in perchloric acid solution. In both the absence and the presence of adsorbed CO, the Ru(0001) electrode shows the potential-dependent formation of well-defined and ordered oxygen-containing adlayers. At low potentials (e.g., from −80 to +200 mV vs Ag/AgCl), a (2 × 2)-O phase, which is unreactive toward CO oxidation, is formed, in agreement with UHV studies. Increasing the potential results in the formation of (3 × 1) and (1 × 1) phases at 410 and 1100 mV, respectively, with a concomitant increase in the reactivity of the surface toward CO oxidation. Both linear (COL) and three-fold-hollow (COH) binding CO adsorbates (bands at 2000−2040 and 1770−1800 cm-1, respectively) were observed on the Ru(0001) electrode. The in situ FTIR data show that the adsorbed CO species remain in compact islands as CO oxidation proceeds, suggesting that the oxidation occurs at the boundaries between the COads and Oads domains. At low CO coverages, reversible relaxation (at lower potentials) and compression (at higher potentials) of the COL adlayer were observed and rationalized in terms of the reduction and formation of surface O adlayers. The data obtained from the Ru(0001) electrode are in marked contrast to those observed on polycrystalline Ru, where only linear CO is observed.

The underpotential deposition of Cu onto Au(111) in different electrolytes has been investigated by LEED, RHEED and AES. Ordered layers of (√3 × √3) R30° and (2.2 × 2.2) type were found for Cu at medium coverages in sulfate and perchlorate solutions, respectively. The formation of different superstructures in different electrolytes is caused by the specific adsorption of the anions.

The cyclic current-potential curve for a well-defined Ru(0001) surface in 0.1 M HCIO4 solution clearly exhibits hydrogen and O/OH adsorption peaks at -0.15 and 0.25 V, respectively. The coulometric charge of the current peak at -0.15 V equals 120 muC cm(-2) corresponding to 0.5 monolayer (ML) H coverage. Both voltammetric peaks disappear completely by the CO electrosorption at -0.1 V, demonstrating that the electrosorbed CO completely blocks H adsorption. The disappeared H adsorption current peak due to the electrosorbed CO corresponds to a CO saturated coverage of 0.5 ML on Ru(0001) in good agreement with the coulometric data determined by the current transient of CO electrooxidation. The coverage of the electrosorbed CO also agrees well with the data obtained for the coadsorption system CO + O/Ru(0001) under UHV conditions. At 0.4 V no CO electrosorption takes place on a (1 x 1)-O/Ru(0001) surface in a CO-saturated HClO4 solution similarly as with CO adsorption on a (1 x 1)-O/Ru(0001) surface under UHV conditions. On the other hand, the coadsorption of COad with O-ad at 0 V gives rise to a well-ordered (2 x 2)-(0 + 2CO) structure similar to that observed from the coadsorption of CO and 0 on Ru(0001) under UHV conditions. No CO electrooxidation occurs at 0.45 V for the coadsorbed CO and 0 on Ru(0001) electrode surface. Up to 0.55 V the CO oxidation rate increases markedly with increasing potential in good agreement with our previous in situ IR results. The driving force for the CO electrochemical reaction is attributed to the decrease in the activiation barrier for CO oxidation by the polarization potential