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

The effect of cooling environment on flame-annealed, stepped Pt{100} electr odes has been investigated using a combined UHV-electrochemical approach. F or 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 therm ally metastable and upon heating to > 800 K it transformed itself irreversi bly into a "hex"-type (Pt{13,1,1}, Pt{11,1,1}, Pt{911} and Pt{711}), an inc ommensurate "(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 incomme nsurate "(1 x 3)" phases undergo a reversible phase transition to a (1 x 1) structure for T > 900 K. Voltammetric characterisation of the hydrogen-coo led crystals gave rise to sharp, well-defined peaks, the magnitudes of whic h correlated strongly with the average terrace width of the (I x 1) structu re. 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 co ntrast, 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, s tepped crystals all undergo surface reconstruction, we suggest that these n ew voltammetric features are "fingerprints" of the clean surface reconstruc tion being lifted by the adsorption of one monolayer of electrosorbed hydro gen to give a somewhat disordered (1 x 1) phase.