Electrochemical study of step reconstruction on platinum surfaces belonging to the [0 [formula omitted]1] zone between Pt(311) and Pt(111)

Abstract

In this paper we present experimental results concerning the effect of thermal and electrochemical oxygen adsorption on the surface structure of platinum faces vicinal to Pt(111) in the [0 1 1] zone whose ordered equilibrium surface structure, when clean, is denoted by Pt(S)[ n (111)×(100)]. Two different types of electrochemical behaviour have been observed depending on terrace width. Under the effect of oxygen adsorption, surfaces with n ⩾ 4 develop a well-marked adsorption state at 0.115 V which reflects the formation of (110) sites to the detriment of the (100) step sites which would normally correspond to the orientation of the sample. This phenomenon can be avoided by cooling the sample under an H 2 + Ar atmosphere, or the step order can be almost totally restored by applying a fast cycling treatment under the same conditions as those used to restore the two-dimensional long-range order in Pt(100) samples. A hard-sphere model of the perturbed surfaces based on a (100) step reconstruction is used to analyse quantitatively the corresponding voltammograms leading to results in agreement with the geometry of the (110) kink sites formed after oxygen desorption. The electrochemical behaviour of orientations with n ⩽ 4 has also been studied. The absence of the adsorption state related to (110) sites after oxygen adsorption-desorption indicates the stabilization of (100) sites when narrow terraces are intrinsic to the orientation of the sample. For Pt(311), representing the turning point of the [0 1 1] zone, analysis of the voltammograms obtained after thermal or electrochemical oxygen adsorption reveals the existence of a microfaceting process leading to the formation of multi-atomic (100) and (111) microfacets no wider than three or four atomic rows.