Influence of steps on the electrochemical oxidation of CO adlayers on Pd(111) and on Pd films electrodeposited onto Au(111)

Electrochemically deposited palladium monolayers on well-ordered and on vicinal Au(111) electrodes have been characterised in sulphuric acid solution by cyclic voltammetry. The electrochemical behaviour of these pseudomorphically grown palladium overlayers is compared with that of a well-ordered and a previously oxidised Pd(111) electrode for hydrogen adsorption, sulphate adsorption as well as for surface oxide formation. A strong impact of the surface defect density was observed for the latter reaction. The electrooxidation of irreversibly adsorbed carbon monoxide monolayers on the various palladium surfaces was studied by cyclic voltammetry and chronoamperometry. The oxidation kinetics are strongly dependent on the number of monoatomic high steps, that act as nucleation centres for adsorbing oxygen-containing species and allow for an anodic stripping of carbon monoxide at more negative potentials than oxidation on terraces. A tailing in the chronoamperometric transients at 0.65 V vs. SCE for the palladium surfaces suggests that diffusion of the reacting species on the terraces is rate-determining.