Abstract
Abstract We investigated a Pt(1 1 1) electrode covered by two-dimensional nanosized Ru islands and used CO chemisorption, cyclic voltammetry and sum-frequency-generation (SFG) to probe the distribution of CO binding sites on such surfaces. Two distinctive CO species were resolved spectroscopically: Pt(1 1 1)/Ru–CO, with CO chemisorbed on the surface ruthenium sites; and Ru/Pt(1 1 1)–CO, with CO chemisorbed on the platinum sites. Our SFG assignment of these species is that the 1970 cm −1 peak corresponds to linear-bonded CO on the Ru island sites and 2070 cm −1 to the linear-bonded CO on the Pt(1 1 1) sites. Further, two current-potential voltammetric peaks from Pt(1 1 1)/Ru–CO, at ≈0.55 and 0.67 V vs. RHE, are associated with SFG resonances at 1970 and 2070 cm −1 . Upon positive going CV scan, the first peak was selectively removed, and the SFG spectrum confirmed that only the resonance from CO chemisorbed on Pt remained, although there was noticeable spectral intensity reduction and spectral tailing, which will have to be reconciled in future research. Clearly however, it is possible to remove CO from the Ru sites while the Pt sites remain occupied by CO, and the remaining CO contribute to SFG and voltammetry without participation of the CO previously present on the Ru sites.
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