The adsorption of ethene on vicinally stepped electrode surfaces and the effect of temperature

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The effect of steps on the adsorption of ethene on platinum electrodes and their effect on the cathodic desorption products have been examined using differential electrochemical mass spectrometry (DEMS). At room temperature, nearly one third of the adsorbate can be desorbed as ethane or butane from the stepped Pt(3 3 2) = Pt(s)-[6(1 1 1) × (1 1 1)] surface during cathodic potential sweeps, as compared to ca. 90% from flat Pt(1 1 0) and only a negligible desorbed amount from Pt(1 1 1). The amount of cathodically desorbed ethene was shown to depend directly upon the number of step sites on the investigated platinum electrode surfaces (Pt(1 1 1), Pt(6 6 5), Pt(3 3 2) and Pt(1 1 0)). The results obtained with Pt(3 3 2)-surfaces very much resemble those obtained before with roughened Pt(1 1 1). This is explained by the structure of such an electrode as revealed by STM. At lower temperature, the amount of cathodically desorbed species is larger. Hence, the corresponding adsorption state (possibly di-σ-bound ethene) is more populated as compared to the strongly adsorbed state (possibly ethylidyne). Besides di-σ-bound ethene another type of adsorbate in a weakly bound state (probably π-bound ethene) was detected. This weakly bound adsorbate could be displaced by adsorbing Cu ions from solution which form a Cu-UPD layer. The amount of such weakly bound ethene equals approximately one tenth of the adsorbate on all surfaces, i.e. it is independent of surface structure.