CO oxidation on stepped Rh[n (111)×(111)] single crystal electrodes: a voltammetric study

Mechanisms of Carbon Monoxide and Methanol Oxidation at Single-crystal Electrodes

“…4b. The voltammograms differ in a number of ways from those recorded in sulfuric acid: first, similar to CO stripping on Pt[n(111) · (111)] electrodes [35], the onset of the oxidation peaks lie at lower potentials in [30,34] perchloric than in sulfuric acid media. The faster oxidation is also observed in the number of scans needed for complete adlayer stripping, which requires only up to three cycles in perchloric media for the surfaces studied.…”

“…The blank cyclic voltammograms show a distinct increase in the reversibility in the hydrogen/(bi)sulfate region (0.05-0.20 V) with increasing step density [30]. Also, the total integrated charge under the hydrogen/ (bi)sulfate peaks was found to decrease with increasing step density, indicating that (bi)sulfate adsorption preferably takes place on the terraces rather than on the steps and defects.…”

“…To systematically investigate the mechanism and the kinetics of the electrochemical oxidation of CO on rhodium electrodes, voltammetric [30] and chronoamperometric [31] studies were performed on a number of Rh[n(111) · (111)] single-crystal electrodes (Rh(331), Rh(553), Rh(554), and Rh(111), with n = 3, n = 5, n = 10, and n = 200-500, respectively), which, like Pt[n(111) · (111)] are composed of terraces of (111) orientation of (n -1) atoms wide separated by monoatomic steps of (110) orentiation. A significant complication in studying the oxidation of CO on Rh is the fact that the CO electrooxidation potential overlaps with the surface oxidation potential, causing surface disordering to occur simultaneously with the oxidation of CO.…”

Mechanisms of the Oxidation of Carbon Monoxide and Small Organic Molecules at Metal Electrodes

“…The idea of a highly mobile CO chemisorbate is always inconsistent with a N&G model, because in the N&G model the assumption of immobile reaction partners is essential. This does not prove that the mean field model is quantitatively correct, although clearly the fit is very good, but merely that on the electrodes that we have studied, there is no physical basis for the key assumption in the N&G model, namely the supposed surface immobility of adsorbed CO. Interestingly, in later work on stepped rhodium single-crystal electrodes [Housmans et al, 2004;Housmans and Koper, 2005a, b], experiments do suggest a low CO mobility. The chronoamperometric transients for rhodium are very different from those obtained for platinum, and a consistent kinetic modeling is quite a bit more involved, as will be discussed in Section 6.2.2.…”

“…From earlier work on the CO electro-oxidation on single-crystal Rh, it is known that the reaction is much slower than on Pt, and that the stripping of a CO adlayer may take several cyclic voltammetric scans to completely oxidize CO ads , from about 30 on Rh(111) to 1 -2 on Rh(110) [Gomez et al, 1997;Housmans and Koper, 2004]. Housmans and Koper studied this reaction in H 2 SO 4 by chronoamperometry [Housmans and Koper, 2005a].…”