Chizuko Nishihara

Formation and desorption of aluminum hydride from hydrogen adsorbed aluminum surfaces

Abstract Hydrogen adsorbed Al single crystal surfaces have been investigated under ultra-high vacuum by thermal desorption (TD) and X-ray photoelectron spectroscopy (XPS). The desorption of an aluminum hydride at 340 K was observed to be zero-order by TD experiments of an Al(111) surface on which hydrogen adsorbed at 150 K. This is a first observation of the desorption of a metal from a hydrogen adsorbed metal surface. XP spectra of A12p for hydrogen adsorbed Al film on Mo(111) indicated that the precursor of the desorbed aluminum hydride, which desorbed as zero-order, was formed with an increase of the temperature of the Al film up to 340 K.

Contributions to the theory of kinetic and catalytic currents in polarography

Summary A rigorous theory of the polarographic kinetic currents, which is valid without limitation in the magnitude of the relevant rate constant, is developed for the first-order preceding chemical reaction proceeding at the expanding plane electrode. The simple, approximate equations with reasonable accuracy are presented for the instantaneous and average values of kinetic currents. They hold within maximum error of 2–3%, provided that the height of the kinetic current is larger than about one-tenth of the corresponding diffusion current. For the catalytic currents, on the other hand, on the basis of the numerical tables given by Koutecký and Henke and Hans simple algebraic expressions are also presented for the instantaneous and average currents, which hold within less than 1% error.

Underpotential deposition of copper on Pt(S)-[n(111) × (100)] electrodes in sulfuric acid solution

Abstract The voltammetric behavior of the underpotential deposition (UPD) of copper in sulfuric acid solutions on a series of stepped surfaces ( n = 3.5, 5, 6.5, 9, 19, 40, ∞ for n (111) × (100)) has been examined in detail. The results are compared with hydrogen adsorption-desorption voltammograms. The potentials of anodic peaks and cathodic peaks coincide for very low potential scan rates except in one case where the anodic peak potential is about 10 mV positive of the cathodic peak potential on the wide terrace of (111) at 0.05 mV s −1 . Copper UPD in sulfuric acid solution is a very slow process. It is shown that step structures profoundly affect the behavior of copper UPD.

Behavior of hydrazine and its effects on the adsorption of hydrogen at Pt(322) and Pt(111) electrodes in sulfuric acid solutions

Abstract The voltammetry of Pt(322) and Pt(111) electrodes in 0.5 M H2SO4 solution was studied in the presence and absence of hydrazine. The amount of hydrazine adsorbed was measured by its oxidation reaction. The effects of the adsorbed hydrazine on hydrogen adsorption—desorption behavior were investigated intensively. Hydrazine adsorbs on both step and terrace sites between 0.10 and 0.30 V (vs. RHE). The saturation amounts at these two sites differ depending on the electrode potential. The oxidation potential of hydrazine on step sites is 0.2 V more positive than that on terrace sites. Hydrazine adsorbs preferentially on step sites. The shapes of the hydrogen adsorption—desorption voltammograms are strongly affected by the adsorption of hydrazine on step sites. At potentials between 0.2 and 0.3 V hydrazine repels hydrogen atoms from step sites and is adsorbed itself instead. Hydrogen atoms can adsorb on step sites in the potential range where hydrazine does not adsorb. One hydrazine species (N2H4 or N2H5+) replaces about four hydrogen atoms on the step sites. Hydrazine adsorbs on terrace sites of Pt(322) and Pt(111) electrodes in the potential between 0.1 and 0.3 V. The behavior of hydrogen adsorption on Pt(322) terrace sites is not changed by the adsorbed hydrazine.

Electrode kinetics of the acetylacetonate complexes of nickel(II) at the dropping mercury electrode

Summary The polarographic and chronopotentiometric behavior of nickel(II)-acetyl-acetonate complexes is examined in the pH-range 3.6–9.8. By analysing the dependence of the d.c. polarographic current-voltage curves on the pH-value, the mechanism of the electrode reaction is elucidated and the relevant kinetic parameters, i.e. , the transfer coefficients and the electrode reaction rate constants, are evaluated. For the preceding chemical reactions involved, the rate and equilibrium constants are determined by analysing the chronopotentiometric I τ 1/2 − I curves. The results obtained are summarized by the reaction scheme illustrated in Fig. 13.

Note on the hydrogen adsorption—desorption voltammogram on Pt(111) in sulfuric acid solution

The remarkable shapes of hydrogen adsorption-desorption voltammograms of basal planes of platinum single crystal electrodes have been noted since the first reports by Clavilier’s group [1,2]. Special attention has been paid to the sharp peaks observed at 0.45 V vs. RHE on Pt(ll1) in 0.5 M sulfuric acid solution. In order to understand the structure of the interface between Pt(ll1) and sulfuric acid solutions, many attempts have been made by applying different instrumental techniques, such as Auger electron spectroscopy, low energy electron diffraction [3], infrared (IR) absorption spectroscopy [4,5], second harmonic generation 161, Uv/Vis reflectance [7], scanning tunneling microscopy (STM) [S] and radioactive labeling [9]. Despite these efforts, we do not have a complete and clear picture of the behavior of the hydrogen atom, water, and anions of sulfuric acid and of the surface structure of Pt(ll1). For details of the electrochemistry at the platinum single crystal surfaces a well documented article [lo] should be referred to. In this note we show some findings on the hydrogen adsorption-desorption voltammograms and on the admittance plots at Pt(ll1) in sulfuric acid solution.

HREELS study on hydrogen adsorbed Al(111) surface

Abstract Recently we have confirmed that aluminium hydride desorbs around room temperature from hydrogen adsorbed Al(111) surface by thermal desorption spectroscopy (TDS). In this study, adsorbed states of hydrogen atoms on Al(111) were investigated, from 85 K to the desorption temperature, by use of high resolution electron loss spectroscopy (HREELS). The loss features observed in the HREEL spectra were assigned based on the local density functional (LDF) calculation. It was revealed that two or three hydrogen atoms adsorb on an aluminium terminal site at low temperature (

Detection of nitrosobenzene as an intermediate in the electrochemical reduction of nitrobenzene on Ag in a flow reactor

Identification du nitrobenzene lors de la reduction electrochimique du nitrobenzene. Utilisation de la chromatographie HPLC couplee a un reacteur electrochimique a ecoulement

Reduction of nitrobenzene in aqueous alkaline solution at an Ag electrode: Observation by SERS, RRDE and UV absorption

Abstract The reduction of nitrobenzene in aqueous alkaline solution at an Ag electrode has been studied. The reduction products detected by a rotating ring—disk electrode (RRDE) and UV absorption were phenylhydroxylamine and aniline. Surface species were observed by surface-enhanced Raman scattering (SERS). At a potential between −0.40 and −0.55 V (vs. SCE) two different SERS spectra of trans-azobenzene were observed. The behaviour of these spectra is discussed.

Crystal faces of anhydrite (CaSO4) and their preferential dissolution in aqueous solutions studied with AFM

Abstract Structures of cleaved surfaces of anhydrite were studied with atomic force microscopy (AFM) before and after partial dissolution in aqueous solutions of NH4Cl and NaHSO4. Two crystal faces showed atom-resolved images just after cleavage, (100) and (010), of which the former was roughened by the dissolution, while step structures were developed on the latter. After dissolution, steplines ran along the a- and c-axes on the (010) face, while they ran in directions inclined to these axes before. It was revealed that the arrangement of dipoles is a key factor in determining stabilities of step structures on crystal faces. On the terraces, the arrangement of oxygen atoms of the sulfate groups and calcium ions were clearly observed.