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 (OH ad ), H 2 O, and/or H 3 O + 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 HClO 4 , SO 4 2− (or HSO 4 2− ), H 2 O (or H 3 O + ), and/or OH ad 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 H 2 SO 4 . The interlayer expansion (d 12 ) 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 (OH ad , H 2 O, and/or H 3 O + ) in the HClO 4 and due to the SO 4 2− (or HSO 4 −) and H 2 O (or H 3 O + ) adsorption in the H 2 SO 4 . 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.
The structure, composition, and electronic state of electrochemically lithiated Si(111) were investigated by using soft X‐ray emission spectroscopy (SXES) combined with scanning electron microscopy (SEM) and by using X‐ray diffraction (XRD) with synchrotron radiation (SR). When the SXES results were compared with the calculated density of state (DOS), we found that three kinds of electrochemically lithiated Si (EC‐LiSi) phases were formed on the Si(111) substrate, that is, a single‐crystalline Li15Si4 (sc‐Li15Si4) alloy phase, an amorphous phase of Li15Si4 and/or Li13Si4 (a‐Li15Si4 and/or a‐Li13Si4), and a mixed phase of a‐Li15Si4 and/or a‐Li13Si4 (52 %) and crystalline Si (c‐Si) (48 %),. The shape of the sc‐Li15Si4 phase was a micrometer‐sized, three‐fold‐symmetric triangular pyramid, which reflects the atomic arrangement of the Si(111) surface, and the XRD patterns, obtained by using SR, revealed that the crystal orientation of sc‐Li15Si4 is in the same direction as the Si(111) substrate. Based on the band center energy shifts, we confirmed that electrons are partially transferred from Li to Si atoms in the LixSi alloy.
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