Electrochemical and UHV characterisation of stepped Pt{100} electrode surfaces

Abstract

The effect of cooling environment on flame-annealed, stepped Pt{100} electrodes has been investigated using a combined UHV-electrochemical approach. For crystals cooled in hydrogen and subsequently transferred to UHV, (1 × 1) LEED patterns are always observed. The (1 × 1) phase was found to be thermally metastable and upon heating to >800 K it transformed itself irreversibly into a “hex ”-type (Pt{13,1,1}, Pt{11,1,1}, Pt{911} and Pt{711}), an incommensurate “(1 × 3)”(Pt{511}) or a commensurate (1 × 2)(Pt{311} and Pt{211}) reconstructed clean surface phase. The reconstructed (1 × 2) and incommensurate “ (1 × 3)” phases undergo a reversible phase transition to a (1 × 1) structure for T>900 K. Voltammetric characterisation of the hydrogen-cooled crystals gave rise to sharp, well-defined peaks, the magnitudes of which correlated strongly with the average terrace width of the (1 × 1) structure. Therefore, it is concluded that cooling of stepped surfaces vicinal to the Pt{100} plane in hydrogen results in unreconstructed (1 × 1) phases in aqueous electrolytes in agreement with previous findings for Pt{100}. In contrast, cooling in ultra-pure argon gives rise to new voltammetric features on the first negative-going potential sweep, analogous to those found for argon-cooled Pt{100}. Together with LEED/AES data showing that the clean, stepped crystals all undergo surface reconstruction, we suggest that these new voltammetric features are “ fingerprints” of the clean surface reconstruction being lifted by the adsorption of one monolayer of electrosorbed hydrogen to give a somewhat disordered (1 × 1) phase.