Shinobu Toshima

Electrochemistry of Prussian Blue Modified Electrodes: An Electrochemical Preparation Method

A new type of Prussian blue modified electrode is described. The Prussian blue modified electrode is electrochemically prepared in a solution of ferric‐ferricyanide. The amount of Prussian blue on electrodes such as platinum, glassy carbon, and is easily controlled by changing the current density, the electrode potential, and the time of the electrolysis. The waves observed at +0.2 and +1.0V vs. SCE are due to the reduction and the oxidation of the ferric part and of the ferrous part in the Prussian blue crystal, or , respectively. This electrode exhibits excellent stability in aqueous solution. A spectroelectrochemical property of the modified electrode is also described.

Prussian‐blue‐modified electrodes: An application for a stable electrochromic display device

An electrochromic display based on a Prussian‐blue‐modified electrode is described. Prussian blues are deposited electrochemically in a solution of ferric‐ferricyanide. Current flow at +0.2 and +1.0 V is due to the reduction of Fe3+ and the oxidation of Fe2+ in the Prussian‐blue coating, respectively. The result is a display that switches from clear to blue, has high stability, and has a response of less than 100 ms.

Formation of intramolecular exciplexes in electrogenerated chemiluminescence

Abstract Electrogenerated chemiluminescence of (9-anthracene)-(CH 2 ) n -(N,N-dimethylaniline) ( n = 0, 1, 2) is discussed. In the electrogenated chemiluminescence spectra, only intramolecular exciplex fluorescence was observed and the local excited fluorescence bands, which were obtained by means of photoexcitation, could not be detected. The efficiency of n = 0 was very large (1.1%) compared with that of the ordinary electron transfer luminescence between the radical anions of aromatic hydrocarbons and the radical cations of aromatic amines (A −1 /D + systems). The intramolecular exciplexes seem to be directly formed by electron transfer reactions.

Electrogenerated chemiluminescence with solvated electrons in hexamethylphosphoroamide (HMPA)

Abstract The electrogenerated chemiluminescence of N-toluenesulfonyl carbazole, 9-chlorofluorene derivatives and N,N,N′,N′-tetramethyl- p -phenylenediamine (TMPD) with solvated electrons in HMPA are discussed. The fairly bright emissions occurred simultaneously when solvated electrons were generated electrochemically. In the case of N-toluenesulfonyl carbazole and 9-chlorofluorene derivatives, the respective carbanions formed by “dissociative electron transfer reactions” are the fluorescents. The singlet state of TMPD seems to be directly formed by the electron transfer reactions between radical cations of TMPD and solvated electrons.

Electrochemical study of UO22+-UO2+-UO2 system in molten LiCl+KCl eutectic

Abstract The redox system UO22+-UO2+-UO2 in LiCl+KCl eutectic has been studied with potentiometry, normal pulse polarography and cyclic voltammetry on glassy carbon and tin oxide electrodes. In the electroreduction of UO22+ taking place in two steps via the intermediate UO2+, the standard potential of UO2+/UO2, E0 (UO2+/UO2), was found to be more positive than E0 (UO22+/UO2+; E0 (UO22+/UO2+)=−0,487 V, E0 (UO2+/UO2)=−0.049 V and E0 (UO22+/UO2)=−0.268 V vs. 1 M Pt(II)/Pt at 450°C (on the molarity scale). The equilibrium constant of the disproportionation reaction (UO22++UO2=2 UO2+) was calculated at K=10−3.0 mol dm−3 at 450°C. On the basis of the data presented, a potential-pO2- diagram of uranium was constructed. Instability of UO2+ was confirmed by the kinetic study, as well as by thermodynamic considerations. The diffusion coefficients of UO22+ and UO2+, and the deposition of UO2 with and without nucleation overvoltages were also described.

Adsorption of divalent cations on tin oxide electrodes in aqueous solutions

The flat band potentials of Sb-doped SnO2 electrodes have been measured in buffer solutions with pH higher than pHpzc both in the absence and the presence of divalent cations such as Mg2+, Ca2+, Ba2+ and Sr2+. The flat band potentials were found to shift toward negative potentials in the presence of the divalent cations. This cation effect is accounted for in terms of the specific adsorption on the oxide surface. The flat band shift (ΔVf) depends on solution pH, measuring time and the cation species. These effects are discussed, referring to comparative studies carried out in colloid systems.

Behavior of semiconductive tin oxide electrodes in molten lithium chloride+potassium chloride eutectic

Abstract In molten LiCl+KCl eutectic at 450°C, current and differential capacity were measured with the potentiodynamic method at Sb-doped polycrystalline tin oxide films prepared on Pyrex glass substrates. SnO2 electrodes usable in high temperature melts were constructed with special care to keep a definite working area. The melt-stable and semiconductive oxide shows a stable polarizable potential region with a span of about 1 V from chlorine evolution to cathodic decomposition of the oxide. Small residual current in the polarizable region indicates a possibility to use the oxide as an indicator electrode in the melt. The interfacial capacity is assigned to the space charge capacity of the electrode side and its potential dependence is explained using the Mott-Schottky equation. A linear Mott-Schottky plot was obtained after several potential scans and the flat band potential was estimated as −1.29 V vs. 1 M Pt-(II)/Pt. The oxide surface in contact with the melt is subject to change during scanning in order to establish a stable melt-oxide interface where the specific adsorption of Cl− ions plays an important role for the stabilization.

Semiconducting tin oxide electrodes in molten sodium chloroaluminate at 175°C

Electrode behavior of Sb-doped poly-crystalline tin oxide electrodes has been investigated by means of current and differential capacity measurements in molten chloroaluminate melts (AlCl3+NaCl) with different pCl values. The SnO2 is stable in the melts consisting of near equimolar composition, being used as an indicator electrode possessing a polarizable potential region between chlorine evolution and its cathodic decomposition. The differential capacity is assigned to the space charge layer capacity of the electrode side and its potential dependence is explained by using the Mott-Schottky equation. It is found that the flat band potential does depend on pCl (=−log aCl−) at a rate of 2(2.3kT/e) per pCl unit. This anomaly is attributed to the specific adsorption of Cl− ions on the oxide electrode.

A study of carbon surfaces in molten LiCl-KCl eutectic-currentless deposition of precious metals on glassy carbon substrates

Abstract Currentless deposition of precious metals, Au, Pt, Ir, Ru, Rh and Pd, on glassy carbon surfaces in LiCl-KCl eutectic at 450°C has been reported. When the electrodes are simply immersed in the melt solutions containing the metal ions, metal deposits equivalent to several atomic layers are obtained within a few minutes. Chronopotentiometric stripping of deposited metals and the decays of open-circuit potentials during the soaking experiments strongly suggest that the deposition is related to the surface redox properties of carbon substrates. Interpretation of the deposition process based on the mixed potential concept is presented, and the substrate reactivity derived from the deposited amount is ascribed to the surface redox reactions involving bulk O 2− ions, superficial water and surface functional groups.

Pulse polarography of uranyl(VI) in molten LiClKCl eutectic

The electrochemical characterization of redox couple UO22+/UO2+ in LiClKCl eutectic at 450°C has been carried out with normal pulse polarography on Pt, Au, tin oxide and glassy carbon electrodes. Pt and Au electrodes immersed in the melt containing UO22+ result in mixed potential systems, being corroded considerably with the simultaneous reduction of UO22+ at the open potentials. While the latter two electrodes give well-defined, two steps reduction waves; the first one is a reversible, one-electron transfer with E12 = −0.487 ± 0.005 V vs 1M Pt(II)/Pt, and the second wave, whose onset potential largely depends on the kind of electrode, is ascribed to a succeeding one-electron transfer yielding UO2 deposits. Pulse polarography on GCE, which has the largest nucleation overvoltage among them, was proved suitable for detection of the intermediate UO2+.