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

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 x 1) LEED patterns are always observed. The (1 x 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 x 3)(Pt{511}) or a commensurate (1 x 2)(Pt{311} and Pt{211}) reconstructed clean surface phase. The reconstructed (1 x 2) and incommensurate (1 x 3) phases undergo a reversible phase transition to a (1 x 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 (I x 1) structure. Therefore, it is concluded that cooling of stepped surfaces vicinal to the Pt{100} plane in hydrogen results in unreconstructed (1 x 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 x 1) phase.