Thickness dependent electrochemical reactivity of epitaxially electrodeposited palladium thin layers on Au(111) and Au(100) surfaces

Electrochemical characteristics of ultra thin Pd epitaxial layers deposited electrochemically on Au(111) and Au(100) surfaces were found to be strongl y dependent on the surface structure and the thickness of the Pd thin layer s. The electrochemical characterizations demonstrate that the Pd/Au(111) an d Pd/Au(100) surfaces behave essentially like Pd(111) and Pd(100) surfaces, respectively. Formation and reduction of oxide on the Pd sub-monolayer sur faces took place at more and less positive potentials, respectively, than t hose on the surfaces of the Pd multilayer. The Pd/Au(100) electrode shows a much higher electrocatalytic activity for the oxidation of formaldehyde th an that at the Pd/Au(111) electrode. Furthermore, the highest activity for the electro-oxidation of formaldehyde was observed at the Pd/Au(100) electr ode when the thickness of the Pd thin layers was less than a monolayer. Thi s behavior was discussed in terms of the potential- and thickness-dependent oxide formation-reduction on the Pd thin layers. (C) 2001 Elsevier Science B.V. All rights reserved.