Toyohiko Nishiumi

Doping reaction of redox-active dopants into polyaniline

Acid doping of functional protonic acids such as ferrocene sulfonic acid, hydroquinone sulfuric acid, anthraquinone sulfonic acid and phenylazobenzene sulfonic acid as dopants in polyaniline takes place homogeneously and the dopant is incorporated at ca. 100% efficiency(1 dopant/polyaniline 2 units). The doping reaction is dominated by diffusion kinetics, which is influenced by the dopant size. The resulting polyanilines have high conductivity of 10−4–10 S/cm similar to that of perchlorate doped polyaniline. Polyaniline doped with redox dopants shows a multiple redox couple in acidic solution, which is applicable to a charge storage system with high energy density. Copyright

Examination of the Gouy–Chapman theory for double layer capacitance in deionized latex suspensions

Electric double layer capacitance at platinum electrodes is controlled by dipole moments of the solvent in the diffuse layer rather than that by ionic distribution, being different from that at mercury electrodes. The controlling step is found by comparing capacitance vs. electrode potential curves in ionic solutions with those in deionized latex suspensions. The curves do not involve a valley shape of Gouy–Chapman (GC)-Sterns type until ionic concentrations are less than 0.05 mM, because measured capacitance is controlled by the inner layer. The valley shape at low concentrations can be measured in deionized sulfonic latex suspensions, whose conductance is brought about by the ionic latex particles rather than the dissociated hydrogen ions. An expression for the capacitance by the ionic latex suspension is derived, which is demonstrated to be the same form of the potential dependence as for mono-valence ions. Ac-impedance data are obtained at parallel polycrystalline platinum wires without an insulating shield. The valley shape is found, which is analyzed by the inverse plot of the capacitance against the hyperbolic cosine of the dimensionless applied potential. The linearity of the plots seems to support the GC-theory, but the capacitance values are much larger than those calculated from the GC-theory. The extra amount can be attributed quantitatively to the orientation of solvent molecules by combining Debyes theory with the GC-theory.

Electron transfer rate on mixed valence states of Class II/III transition for N, N'-diphenyl-1,4-phenylenediamine structures as a polyaniline unit

Abstract The first example of the determination of the electron transfer rate ( λ , V , Δ G * , k th ) for N , N ′ -diphenyl-1,4-phenylenediamine derivatives using the Marcus–Hush theory is described. These results were in good agreement with the ones obtained using variable-temperature IR spectra measurements.

Reconstruction of gas–liquid flows using the stochastic estimation with a 16-channel electrode array

Bubble-injection methods are considered to be a prospective approach to reduce skin-frictional drag for ships. To apply this technique for unsteady flows, we attempt to introduce a feedback loop of air injection in future applications. Hence, we wish to establish reduced-order models of unsteady bubbly flows from the information at the bottom of the ship, but this must be achieved with a limited number of sensors in practice. This motivates us to develop a reconstruction technique that recovers instantaneous phase information of gas–liquid flows. This study introduces the so-called stochastic estimation and reconstructs bubble distribution based on electrical impedance. We simulate the flow at the bottom of a ship using a horizontal channel and install a 16-channel electrode array on the upper wall to acquire time histories of electrical impedance. The relation between the bubble distribution and the electrical impedance is determined by simultaneous image measurement using a high-speed video camera. Once the coefficients of the linear relation between the electrical impedance and the local void fraction are calculated, two-dimensional bubble distribution can be estimated from only voltages at the 16 electrodes. The proposed technique is examined over a range of void fractions and flow velocities, and the capabilities of the stochastic estimation applied to bubbly flow reconstruction are demonstrated by comparing the reconstructed/predicted images with the original ones.

Fluorescence Switching Based on the Redox Reaction of Quinones Induced by Complexation with Rare-Earth Metals

The fluorescence emission switching behavior based on the redox reaction of quinone-Eu complexes was investigated. The addition of Eu(OTf) 3 caused positive shifts in the potential and induced a fully irreversible two-electron redox reaction around 0.2 V, which is similar to that of the proton. In the presence of Eu(OTf) 3 , the redox reaction of quinones takes place accompanied by Eu 3 + ion transfer, and the redox activation efficiency of Eu 3 + is 100 times greater than that of the proton. The Eu 3 + emission is investigated by complexation with the hydroquinone. Here, we show that we first found this fluorescence switching based on the redox reaction of the benzoquinone-hydroquinone exchange.

Determination of concentration of saturated ferrocene in aqueous solution

The solubility of ferrocene in aqueous solution is known to be approximately 0.04 mmol/dm 3 . The solubility values determined by voltammetry have been overestimated because of adsorption on electrodes. This work deals with discerning diffusion from adsorption by altering not only the voltammetric time scale but also the solvents used. Fast voltammetric responses by differential pulse voltammetry and fast scan voltammetry exhibited adsorption behavior. In contrast, quasi steady-state voltammetry showed the diffusion-control, the current of which seemed to evaluate the saturated concentration accurately. However, the currents in the solution including a small amount of organic solvent were smaller than those in the aqueous solution although the concentrations were identical. Solutions including organic solvents have often been used to obtain calibration curves. Therefore, the concentration evaluated from the calibration curve was estimated to be larger than the true concentration. The current in the organic solvent was explained in terms of the extra solvation energy by supersaturation, which was dissipated to low concentrated domains by diffusion. It was formulated in the form of dif - fusion coefficients. The true concentration was evaluated to be 0.01 mmol/dm 3 by slow scan

Salt-free electrolysis of water facilitated by hydrogen gas in thin layer cell

Correspondence: Koichi Jeremiah Aoki Department of Applied Physics, University of Fukui, 3-9-1 Bunkyo, Fukui, 910-0017 Japan Tel +81 776 27 8665 Fax +81 776 27 8750 Email kaoki@u-fukui.ac.jp Abstract: Electrolysis of water without salt in a thin layer cell requires a voltage of more than 1.3 V. This voltage is found to be reduced to 0.4 V when hydrogen gas is dissolved in electrolyzed water. The decrease in the overvoltage can be used for the salt-free electrolysis of pure water. Thin layer electrolysis under steady state is often caused by redox cycling. The redox cycling model relevant to the reaction between H 2 and H+ is theoretically analyzed here in a two-electrode cell. The validity and limitation are discussed on the basis of the experimental voltammograms of a solution containing H 2 and H+. When a solution contains H 2 without deliberately adding H+, hydrogen gas would not be expected at the cathode due to the small amount of H+. Consequently redox cycling might be blocked. However, experimental voltammograms, without the addition of H+, exhibited the steady state limiting current by redox cycling. The current was regarded as dissociation kinetics of water. The redox cycling in this case was theoretically analyzed to partially explain the experimental results. The oxidation of hydrogen gas at the anode facilitates the dissociation kinetics to produce redox cycling.