CO adsorption and kinetics on well-characterized Pd films on Pt() in alkaline solutions

Abstract

The electrochemistry of CO on a bare Pt(111) electrode as well as a Pt (111) electrode modified with pseudomorphic thin palladium films has been studied in alkaline solution by means of Fourier transform infrared (FTIR) spectroscopy. First Pd films were prepared and well characterized in UHV and subsequently transferred into the electrochemical cell for the registration of the voltammetric profiles. The charge corresponding to the formation of underpotentially deposited hydrogen (H upd ) on these Pt(111)-xPd surfaces was established in sulfuric acid solution as a function of x (0 ≤ x ≤ 1 Pd monolayer (ML)).All subsequent measurements were then performed on electrochemically deposited palladium films using the above H upd -charge vs. Pd coverage relationship to evaluate the amount of electrochemically deposited palladium. FTIR spectra for CO adsorbed on one monolayer and a submonolayer coverage are compared to those of the unmodified Pt(111) surface, all surfaces having identical 2D lattice structures. Infrared absorption bands of CO bound on either Pt(111) or Pt(111)-1ML Pd are clearly 1 distinguished. Spectra of CO adsorbed on Pd submonolayers show characteristic features of both CO bound to Pt and to Pd, indicating that on Pt(111)-xPd surfaces there is no coupling between Pt-CO ad and Pd-CO ad molecules. The kinetics of CO oxidation on these surfaces is determined either by rotating disk electrode (RDE) measurements or by FTIR spectroscopy, monitoring the CO 3 2-production. The oxidation of CO ad on Pt (111) and on Pd modified platinum surfaces starts at the same potential, ca. at 0.2 V. The oxidation rate is, however, considerably lower on the Pt(111)-xPd surfaces than on the Pt(111) surface. The kinetics of CO oxidation appears to be determined by the nature of adsorbed hydroxyl anions (OH ad ), which are more strongly (less active) adsorbed on the highly oxophilic Pd atoms.

Platinum-Enriched Ni/Pt(111) Surfaces Prepared by Molecular Beam Epitaxy: Oxygen Reduction Reaction Activity and Stability

“…Each spectrum is presented here as a ratio of spectra recorded before and after CO exposure. Because exposing the UHV-cleaned Pt single-crystal surfaces to air causes structural changes in their topmost surfaces, 8) the Ni 3.0nm / Pt(111) and clean Pt(111) surfaces were transferred to an electrochemical system set-up in a N 2 -purged glove box. 15) Electrochemical measurements were taken using a conventional electrochemical cell that included a platinum-made counter electrode and a reversible hydrogen electrode (RHE).…”

The effect of specific chloride adsorption on the electrochemical behavior of ultrathin Pd films deposited on Pt() in acid solution

“…FTIR characterization of CO ad on Pt(111) modified with 0ML < Θ Pd < 1ML was used as an indirect probe in order to establish whether Pd forms 2D island or whether the Pd atoms are dispersed on the surface much more randomly, as seen for example for the deposition of Bi on transition metals [19]. The fact that three different C-O stretching bands, corresponding to CO ad on Pd and on the bare Pt substrate, are observed on a Pt(111) electrode partially covered by Pd, indirectly suggested that Pd atoms form islands and that Pt and Pd exhibit their own individual surface chemistry [16,17]. Very recently, it has been proposed that the kinetics of CO oxidation on Pt(hkl) is not governed only by the surface concentration of CO ad and OH ad species, but is also strongly affected by the delicate balance between the coverage of CO ad , OH ad and anions from the respective supporting electrolyte [20].…”

“…For example, the morphology and stability of Pd films on Pt(111) were examined by utilizing in-situ surface x-ray diffraction [11] and FTIR measurements [16,17]. SXS studies demonstrated that both UHV and electrochemically deposited films are pseudomorphic, i.e.…”

Platinum Monolayer Electrocatalysts for the Oxygen Reduction Reaction: Improvements Induced by Surface and Subsurface Modifications of Cores

“…Baldauf and Kolb [54] reported that H absorption (H abs ) occurs only for Pd films thicker than 2 ML. This reversible process that is very similar to the H ads/des occurred on a Pd ML /Pt(111) electrode [55] and therefore is tentatively assigned to H ads/des on a segregated Pd layer on a Pd 3 Fe (111) a Pd/annealed-Pd 3 Fe(111) electrode does not occur until the positive potential limit extends beyond 0.73 V (red and blue line in Figure 16(a)); this indicates the positively shifted onset of oxidation of ∼0.1 V relative to that of Pd(111). The charge density under the cathodic peak at ∼0.73 V, reflecting the surface coverage of oxygen-containing species, is considerably smaller for the Pd/annealed-Pd 3 Fe(111) electrode than for the Pd(111) one (Figure 16(b)).…”