Fusao Kitamura

In situ FT-IR spectroscopic observation of a room-temperature molten salt | gold electrode interphase

We have investigated the molecular structure of an 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) | gold electrode interphase by means of in situ Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). The feature in the FT-IRA spectra obtained suggests that EMI+ present in the interphase orients vertically with the molecular axis in the imidazole ring nearly parallel to the electrode surface in a potential range of −1.3 to +0.6 V vs. Ag|Ag+. The applied electrode potential causes the unbalance of the charge in the interphase, as usually seen in electrolyte solution | electrode interphases.

Multiple voltammetric waves for reductive desorption of cysteine and 4-mercaptobenzoic acid monolayers self-assembled on gold substrates

The reductive desorption of cysteine and 4-mercaptobenzoic acid monolayers formed on polycrystalline and single-crystalline gold substrates has been investigated. Three cathodic waves observed at polycrystalline gold electrodes are correlated with reductive desorption from each small domain of the low index faces, i.e. (111), (100) and (110), over the surface. The stability of the adsorbates differs substantially depending on the surface crystallographic orientation, in the order (111) < (100) < (110). Thus, the reductive desorption occurs at certain potentials, leading to an apparent peak separation on their cyclic voltammograms. Partial desorption of the adsorbate via control of the potential would be a simple and reliable method of fabricating functional electrodes designed for use as electrocatalysts or sensors, on which only the small domains of the (111) face could be selectively exposed to an electrolyte.

Adsorption behavior of viologen derivatives on hanging mercury electrode surfaces

Abstract The adsorption behavior of N , N ′-dialkyl-4,4′-bipyridinium dications (viologens) on hanging mercury electrode surfaces was investigated as a function of the alkyl chain length (C n V 2+ , n = 1–8). Monolayer adsorbed viologens give a pair of very narrow spike-like peaks on cyclic voltammograms, which can be attributed to the redox electrode reaction. The peak location was found to depend on both the alkyl chain length and the bulk concentration, and is shifted to a more positive potential with increasing chain length. These facts suggest strongly that the lateral interaction between alkyl chains of viologen molecules plays an important role in the stabilization of the structure of adsorbed layers.

In situ IR spectroscopic study of water at a polycrystalline gold electrode surface

The effect of the electrolyte anions on the water structure at the interface between a polycrystalline gold electrode and aqueous electrolyte solutions was studied using in situ Fourier transform IR reflection absorption spectroscopy (FT-IRAS). Considerably sharp absorption bands due to OH stretching modes of water were observed in the 3600–3500 cm−1 range in solutions containing F−, Cl−, Br−, I−, BF−4, ClO−4 or PF−6. The band intensity was found to be strongly dependent upon the electrode potential, while the band positions exhibited almost no potential dependence. The bands, however, appeared at different frequencies depending upon the electrolyte anions used, which strongly suggests that these water molecules should be in the hydration spheres of the anions. We also found that the potential dependent adsorption/desorption process of halide ions dominated the spectral feature of interfacial water, which was also supported by the double-layer capacitance measurements.

Characterization of the adsorption state of carbonate ions at the Au(111) electrode surface using in situ IRAS

The spectro-electrochemical behavior of carbonate and bicarbonate ions at the Au(111) electrode surface was studied using the infrared reflection absorption spectroscopy (IRAS). An absorption band caused by the adsorbed carbonate ions was observed in the wavenumber region of 1425–1511 cm − 1 both in Na2CO3 and NaHCO3 solutions. It was concluded that the adsorbed carbonate ions co-ordinate with the electrode surface in the unidentate state with their symmetry axis normal to the substrate. This orientation is retained in the whole potential region where carbonate ions adsorb on the electrode surface in contrast to the behavior of the carbonate ions adsorbed on the Pt(111) electrode surface.

Adsorption of atomic hydrogen on a polycrystalline Pt electrode surface studied by FT-IRAS: the influence of adsorbed carbon monoxide on the spectral feature

Adsorption of atomic hydrogen on a polycrystalline Pt electrode surface was studied by in situ infrared reflection absorption spectroscopy (IRAS). When the electrode potential was adjusted in a potential range where the underpotential-deposited (upd) hydrogen was formed, an absorption band assignable to the vibration of on-top CO (which would be formed by the reduction of a trace of CO2) appeared at ca. 2010 cm−1 even for highly purified 0.1 M (M=mol dm−3) H2SO4 solution. An absorption band due to the on-top H was observed at ca. 2070 cm−1 for a conventional acidic solution in a potential range as narrow as ca. 0.1 V just before the hydrogen evolution reaction (her) ascribable to the reduction of hydronium ions began. On the other hand, the on-top H band was observed unequivocally for a solution containing 1 mM H2SO4 and 99 mM Na2SO4 over a wide potential range where molecular hydrogen was formed by the reduction of hydronium ions. Even for a neutral solution such as 0.1 M KCl, the weak band ascribable to the on-top H was detected. The dependence of the spectral feature on the concentration of hydronium ions and the applied electrode potential strongly suggested that the on-top H is the intermediate in the electrochemical reduction of hydronium ions. We demonstrated that the adsorbed CO is readily formed by the reduction of CO2 in the 0.1 M H2SO4 solution.

Voltammetric and spectroscopic study of the adsorption of alkyl viologens on a HOPG electrode

Abstract Adsorption states of N,N′-dialkyl-4,4′-bipyridinium ions (viologens) and their cation radicals on a highly oriented pyrolytic graphite (HOPG) electrode surface were investigated by cyclic voltammetry and in situ infrared reflection-absorption spectroscopy (IRAS). A pair of spike-like anodic and cathodic waves was observed in the potential region well positive of the first reduction wave for the solution species. The peak potentials were found to depend on their alkyl chain length, and were shifted in the positive direction with the increase in the number of carbon atoms in the alkyl chains. Each pair is ascribed to a one-electron faradaic process of adsorbed viologens. It was indicated from IRAS measurements that the adsorbed cation radicals oriented with their longer molecular axis parallel to the HOPG surface, while the bipyridine ring planes were perpendicular to the surface (side-on configuration).

Oxidative polymerization of p-aminoazobenzene in acetonitrile: A new electroactive polymer

Abstract The oxidative polymerisation of p -aminoazobenzene (PAAB) on glassy carbon in acetonitrile was studied by cyclic voltammetry, the potential step method, and SEM and FT-IR spectroscopy. The presence of a base-like pyridine was found to be essential for the polymerization process. The prepared polymer (poly( p -aminoazobenzene), abbreviated as poly-PAAB) films of thicknesses up to several (μm were found to be very stable and insoluble in aqueous solutions and in common organic solvents, except dimethyl formamide and tetrahydrofuran. The films are electroactive in acidic solutions but electroinactive in acetonitrile. The electroactivity of these films is attributed to a proton + electron addition/elimination reaction at -NH- sites. The capacitive current contribution in the potential region where the films are electroactive is larger than is usually observed for the conventional polyaniline films. The concentration of the electroactive sites in poly-PAAB was found to be about twenty times lower than that of polyaniline while the diffusion coefficient for the charge transport process within the films was found to be four times lower. The azo groups presented in the films were found to be reduced irreversibly in acetonitrile and aqueous acidic solutions. The prolonged reduction of the azo groups was found to lead to the loss of the electroactivity and the slow degradation of the films.

Square wave voltammetric sensing of uric acid using the self-assembly of mercaptobenzimidazole.

The self-assembled monolayer of a heterocyclic thiol, mercaptobenzimidazole (MBI) on gold (Au) electrode is successfully utilized for the voltammetric sensing of uric acid (UA). The self-assembly of MBI separates the voltammetric signal of UA from the interfering ascorbate (AA). Selective detection of UA in the presence of a large excess of AA or the simultaneous detection of UA and AA is achieved at the MBI monolayer-modified electrode. This electrode can detect as low as 1 microM of UA in the presence of 100-fold excess of AA with excellent reproducibility. The practical utility of the electrode is demonstrated by measuring the concentration of UA in human serum.

Two-electron reduction of a Rh-Mo-Rh dithiolato complex to form a triplet ground state associated with a change in CO coordination mode.

We synthesized a dithiolato-bridged heterometal trinuclear complex [{(eta(5)-C(5)Me(5))Rh(S(2)C(6)H(4))}(2)Mo(CO)(2)] (1) in which two rhodadithiolene complex units are bridged by a Mo(CO)(2) moiety. Complex 1 with a Rh(III)-Mo(0)-Rh(III) bond exhibits reversible one-step two-electron reduction with potential inversion. This redox process between 1 and 1(2-) accompanies a reversible structural change, which is an alternation in the CO coordination mode between semibridging and bridging. The ground state of dianion 1(2-) with a Rh(II)-Mo(0)-Rh(II) bond is assigned to spin triplet. These alternations of CO coordination mode and spin state are fully consistent with the density functional theory calculation results. This is the first example of multinuclear metalladithiolene complex which was successful in elucidating a reversible multielectron redox process associated with structural change and spin state change.