Yoshitaka Shingaya

The vibrational spectra of water cluster molecules on Pt(111) surface at 20 K

Abstract The adsorption of D 2 O on Pt(111) at 20 K has been investigated by infrared reflection absorption spectroscopy (IRAS). Water was found to form as a dimer at low coverages and it grew a tetramer molecule at high coverages. The structures of the cluster water molecules on the surface were derived from the intensities and the frequencies of symmetric and asymmetric ν OD stretching absorptions. The annealing at higher temperatures than 130 K was needed to form an ice bilayer island structure.

Comparison of a bisulfate anion adsorbed on M(111) (M=Pt, Rh, Au, Ag and Cu) ☆

Abstract Adsorption of sulfuric acid species on various metal(111) electrodes in a 0.5 M H2SO4 solution was investigated by infrared reflection absorption spectroscopy (IRAS). Pt, Au, Ag, Cu and Rh(111) were used as electrodes. HSO4− is adsorbed on all of the surfaces including Pt, Rh, Au, Ag and Cu in a 0.5 M H2SO4 solution. Considerable amounts of sulfate in addition to bisulfate coexist on Ag(111) in a 0.5 M H2SO4 solution. Also, both DSO4− and SO42− are coadsorbed on Au(111) in 0.5 M D2SO4+D2O solution. The interconversion of HSO4−/H3O+ and H2SO4 that was seen on Pt(111) was not observed on the other electrodes. The frequencies of the SO3 symmetric and S–OH stretching bands of a bisulfate adsorbed on the electrode surfaces are related to the electronic state of each M(111) surface.

In situ and ex situ IRAS, LEED and EC-STM studies of underpotentially deposited copper on a Pt(111) electrode in sulfuric acid solution : coadsorption of sulfate ion with copper

Abstract The electrodeposition of copper on a Pt(111) electrode in sulfuric acid solution was studied by means of voltammetry, in situ and ex situ infrared reflection absorption spectroscopy, in situ electrochemical scanning tunneling microscopy and low energy electron diffraction. At potentials more positive than 0.75 V, LEED and in situ scanning tunneling microscope images showed a ( 3 × 3 ) − R 30 ° structure of bisulfate anions on Pt(111). At the wide potential regions more negative than 0.5 V, images of the ( 2 1 1 2 ) structure were observed from in situ STM and ascribed to a top-layer structure of sulfate anions on UPD copper on Pt(111). Between these potentials where underpotential deposition of copper or copper stripping occurred, the sulfate anion was coadsorbed with a copper ion on a Pt(111) electrode in the ( 3 × 3 ) − R 30 ° structure.

Simulation of the electric double layers on Pt(111)

Abstract The coadsorption of water and sulfur trioxide (SO 3 ) molecules on Pt(111) was studied by thermal desorption spectroscopy, in situ and ultra-high vacuum (UHV)-infrared reflection absorption spectroscopy with the intention of producing a double layer structure on a Pt(111) electrode surface in a 0.5 M H 2 SO 4 acid solution. The vibrational frequencies of water, bisulfate and sulfuric acid molecules adsorbed on UHV model surfaces at temperatures ranging between 110 and 300 K were compared with those from an actual double layer in a 0.5 M H 2 SO 4 acid solution under active potentials. Model structures on Pt(111) under UHV obtained from surfaces after 190 and 260 K annealing coincided well with those from electrode surfaces at a negative and a positive electrode potential, respectively. Sulfuric acid molecules on a Pt(111) electrode observed at 750–1100 mV were reproduced by dehydration from the coadsorbates of H 3 O + and HSO − 4 at 200–300 K.

Upd mechanisms of copper and thallium on a Pt(111) electrode studied by in-situ IRAS and EC-STM

Underpotential deposition (upd) of copper and thallium on a Pt(111) electrode in a sulfuric acid solution were studied by time-resolved in-situ infrared spectroscopy and electrochemical scanning tunneling microscopy. Bisulfate anions adsorbed on a Pt(111) electrode were replaced by copper or thallium ions upon upd. The vS-O stretching frequency of the bisulfate anion adsorbed on a Pt(111) electrode showed drastic changes with these replacements. During copper underpotential deposition (0.5 to 0.8 V vs. SHE), sulfate anions were coadsorbed with copper ions on a Pt(111) electrode in the form of √3 × √7 structure. Even at a potential more negative than 0.5 V, the image of √3 × √7 structure was observed steadily from in-situ STM. The spot in the STM image was ascribed to sulfate anions adsorbed on upd copper on Pt(111). In contrast to the copper upd, sulfate anions coadsorbed with upd thallium on a Pt(111) electrode were likely to desorb in a negative sweep. Various kinds of upd process were classified systematically in terms of interactions exerted for an electrolyte anion, a upd atom and an electrode surface. The roles of an electrolyte anion and an electrode potential are especially important for upd mechanisms, and are discussed in detail.

Infrared spectroscopic study of electric double layers on Pt(111) under electrode reactions in a sulfuric acid solution

Abstract The electric double layer structures on a Pt(111) electrode in H 2 SO 4 solution were studied by in-situ and ex-situ infrared spectroscopies, and the structures were successfully created by a gas phase adsorption of H 2 O and SO 3 under UHV conditions. The absorption bands of hydrogen, neutral water, hydronium cation and bisulfate anion were observed in the in-situ spectra as a function of an electrode potential. Similar spectra could be reproduced by sequential gas doses of H 2 O and SO 3 on Pt(111) at low temperatures under ultrahigh vacuum conditions (ex-situ measurements). The various kinds of electrode reaction were responsible for the real double layer structures as well as the electrode potentials.

Interconversion of a bisulfate anion into a sulfuric acid molecule on a Pt(111) electrode in a 0.5 M H2SO4 solution

The coadsorption of water and sulfur trioxide (SO3) molecules on Pt(111) was studied by thermal desorption spectroscopy, in-situ and non-situ infrared reflection absorption spectroscopy in order to reveal a double layer structure on a Pt(111) electrode surface in a 0.5 M H2SO4 acid solution. The vibrational frequencies of water, bisulfate and sulfuric acid molecules adsorbed on ultra-high vacuum (UHV) model surfaces at temperatures of 110–300 K were compared with those from a real double layer in a 0.5 M H2SO4 acid solution under active potentials. Model structures on Pt(111) under UHV obtained from surfaces after a lower- and a higher-temperature annealing agreed well with those from surfaces at a negative and a positive electrode potential, respectively. A sulfuric acid molecule on a Pt(111) electrode observed at 750–1100 mV was reproduced by dehydration from the coadsorbates of H3O+ and HSO4− at 200–300 K.

Coordination number and molecular orientation of hydronium cation/bisulfate anion adlayers on Pt(111)

The molecular orientation and coordination number of a hydronium cation (H 3 O + ) coadsorbed with a bisulfate anion (HSO 4 - ) and water on Pt(111) were studied by infrared reflection absorption spectroscopy (IRAS) and thermal desorption spectroscopy (TDS). H 3 O + was adsorbed on Pt(111) at 110 K with its molecular C 3 axis perpendicular to the surface. However, the H 3 O + molecule, when coadsorbed with HSO 4 - , changed the molecular orientation on Pt(111) with the C 3 axis parallel to the surface. The hydration number per HSO 4 - or H 3 O + on Pt(111) was examined by TDS measurements as a function of θ HSO4 -. The lower and higher HSO 4 - coverages produced larger and smaller amounts of water molecules in the coordination number, respectively. The results agreed well with those of in-situ IRAS.

Coadsorption of ammonia and electrolyte anions on a Pt(111) electrode

The adsorption of NH 3 and the coadsorption of NH 3 and an electrolyte anion on a Pt(111) electrode have been studied by voltammetry and infra-red reflection absorption spectroscopy (IRAS). In IRA spectra of NH 3 adsorbed on a Pt(111) electrode, an absorption band appeared around 1300 cm -1 in a 0.01 M NH 3 +0.1 M HF solution. The band was considerably broad (FWHM is 50 cm -1 ) and showed a frequency shift with an electrode potential change (45 cm -1 V -1 ). The absorption band was assignable to a symmetric deformation mode of NH 3 adsorbed on Pt(111) via a nitrogen lone pair orbital. The formation of hydrogen bonds between NH 3 and H 2 O molecules, which was recognized by the band frequency shift and broadening, was confirmed by the coadsorption study of NH 3 and H 2 O using IRAS under UHV conditions ( UHV modelling). The coadsorption of NH 3 and HSO 4 - was observed by IRAS in the 0.1-0.01 M NH 3 +0. M H 2 SO 4 solution. The band shape of NH 3 coadsorbed with HSO 4 - was extremely sharp. The appearance of the sharp absorption band of NH 3 symmetric deformation mode can be explained by the existence of well-ordered hydrogen bonds. The SO 3 symmetric stretching mode of HSO 4 - coadsorbed with NH 3 exhibited substantially lower frequency shifts compared with that of HSO 4 - alone over the entire potential range. This IRAS result indicates that adsorption strength of the HSO 4 - on Pt(111) is enhanced in the course of the coadsorption with NH 3 .

Vibrational spectroscopic studies of the structure of species derived from the chemisorption of bisulfate anion on a Pt(111) single-crystal electrode

Abstract The structure of bisulfate anion adsorbed on a Pt(111) surface was studied by infrared spectroscopy as well as an ab initio molecular orbital calculation. The calculation predicted the structure and vibrational frequencies of the anion. The band assignments in the infrared and Raman spectra of KHSO4 were carried out by comparing the observed frequencies of the bisulfate anion with those of the calculated values. The single absorption band of bisulfate anion adsorbed on a Pt(111) surface showed a large frequency shift against a potential change (140 cm−1 V−1). The anion chemisorbed through tridentate oxygen coordination on the surface and the band was assigned to the symmetric SO3 stretching mode.