Abstract
The electrochemical behavior of thin Pd films supported on a Pt(1 1 1) electrode is investigated by cyclic voltammetry and in situ Fourier transform infrared (FTIR) spectroscopy. It is demonstrated that in perchloric acid solution underpotential deposition of hydrogen (H upd) and hydroxyl adsorption (OH ad) is in strong competition with the adsorption of Cl − anions, the latter being present as a trace impurity in HClO 4. The interaction of Cl − with Pd is rather strong, controlling the adsorption of H upd and OH ad as well as the kinetic rate of CO oxidation. The microscopic insight (the binding sites) of the adsorbed CO (CO ad) and the rate of CO oxidation (established from CO 2 production) on Pt(1 1 1) modified with a (sub)monolayer of Pd is elucidated by means of Fourier infrared (FTIR) spectroscopy. The appearance of both the characteristic Pt(1 1 1)–CO ad and Pt(1 1 1)–1 ML Pd–CO ad stretching bands on a Pt(1 1 1) surface covered by 0.5 ML Pd confirms previous findings that the Pd atoms agglomerate into islands and that the bare Pt areas and the Pd islands behave according to their own surface chemistry. The systematic increase of the Pd surface coverage results in a gradual change in the catalytic properties of Pt(1 1 1)– xPd electrodes towards CO oxidation, from those characteristic of bare Pt(1 1 1) to those which are characteristic for Pt(1 1 1) covered with 1 ML of Pd.
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