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Potential-dependent structures and potential-induced structure changes of the Pt(111) electrode in perchloric and sulfuric acid electrolyte solutions were investigated in the potential region between the underpotential deposition (UPD) of hydrogen (0.05 V vs RHE) and surface oxide formation (0.95 V) by in situ surface X-ray scattering (SXS) using the electrolyte thickness controllable spectroelectrochemical cell. In both solutions, the interfacial structures, including not only the surface arrangements of the adsorbates but also the Pt(111) surface atomic arrangements at various potentials, were accurately determined and compared with those previously reported in the literature. Several differences and new results when compared to the previously reported results were found by in situ potential-dependent structure measurements as follows: at 0.90 V, while oxygen species, such as an adsorbed hydroxyl group (OHad), H2O, and/or H3O+ with a total coverage of 1 monolayer (ML), are adsorbed on the atop site of the Pt(111)-(1 × 1) surface with the (1 × 1) structure in the HClO4, SO42– (or HSO42–), H2O (or H3O+), and/or OHad with a total coverage of 1 ML are coadsorbed on the atop site of the Pt(111)-(1 × 1) surface also with the (1 × 1) structure in the H2SO4. The interlayer expansion (d12) between the first and second outermost Pt layers is partially relaxed due to the UPD hydrogen desorption and mainly due to the adsorption of the oxygen species (OHad, H2O, and/or H3O+) in the HClO4 and due to the SO42– (or HSO4–) and H2O (or H3O+) adsorption in the H2SO4. These potential-induced structure changes were confirmed by in situ X-ray scattering intensity measurements while maintaining a certain scattering point as a function of the potential.
Kondo et al. (Mon,) studied this question.
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