This paper aims at finding the experimentally controllable variables of solvent for the electric double layer capacitance obtained at two parallel platinum wire electrodes in the polarized potential domain. The equivalent circuit used is the frequency-dependent double layer impedance in series with solution resistance. The evaluated capacitance shows no systematic relation with the dielectric constants, viscosity, boiling temperatures, or dipole moments of the solvents but is proportional to the inverse of the lengths of field-oriented molecules. The proportionality indicates common saturated dielectric constants, 6, of 13 solvents. The variables controlling the capacitance are the saturated dielectric constants and the lengths of solvent molecules along the dipole.
The behavior of electric double layers at polarized interfaces in KC1 solutions is revisited in order to examine properties of the constant phase element (CPE). We pay attention specifically to frequency dependence of both the capacitance and the resistance. Two parallel platinum wires immersed in solution are used as insulator-free * C orresponding author, phone +81
Intramolecular electron transfer (ET) within the class II/III transition for the mixed-valence state of N,N′-diphenyl-1,4-phenylenediamine (PDA) derivatives which were substituted in the center or the outer phenyl ring and N,N′-diphenylbenzidine (BZ) was examined. Each compound showed two reversible redox couples. The splitting of the redox waves, ∆E, is related to the interaction intensity between redox sites. The introduction of a substitutent into the central phenylene ring of the PDAs resulted in a decrease in ∆E. A similar result was noted for the expansion of the distance between the redox centers such as in BZ. In opposition, the ∆E of N,N′-bis(2,6-dimethylphenyl)-1,4-phenylenediamine (2,6-DMPDA) as a compound with substituents introduced into the outer phenyl rings was spread. The mixed-valence state of these compounds also exhibited an intervalence charge transfer (IV-CT) band in the near-IR region which provided the determination of the Marcus reorganization energy (λ), the electron coupling (V), the thermal ET barrier (∆G*), and the electrontransfer rate (k th ) using the Marcus-Hush theory. We first confirmed the electron-transfer rate of PDA derivatives in the class II/III transition state by two methods. The ν(N-H) stretching vibrational spectra of the mixed-valence states were analyzed by a Bloch-type equation analysis using variable-temperature IR spectra measurements which were to be in good agreement with the those obtained from the Marcus-Hush theory. On the basis of this approach, the electron-transfer rate of PDA was determined to be 8.2 × 10 11 s -1 at 298 K, yielding ∆G q ) 420 cm -1 (the activation free energy from the Eyring plot) for the underlying process.
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)-Stern's 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 Debye's theory with the GC-theory.
a b s t r a c tWhen hydrogen gas is bubbled into water, it may well be present as stabilized bubbles rather than hydrated hydrogen molecules, as in the spontaneous emulsification at oil|water interfaces without surfactant. On this prediction, we used dynamic light scattering (DLS) to find bubbles 0.4-0.5 lm in diameter, which were stable for more than 9 h. The intensity of the scattering light, which was proved to be proportional to concentrations of polystyrene latex suspensions, was also kept in solution in contact with hydrogen gas atmosphere. The bubbles were stable even at 50 g (gravity) by centrifugation. Voltammograms of the bubble-included solution had the oxidation peak, of which current was proportional to the intensity of DLS. Concentration of hydrogen in solution was evaluated accurately by comparing voltammetric currents at a regular electrode and a small electrode. The oxidation of hydrogen should be caused by the hydrated hydrogen which was supplied by dissolution of bubbles. Kinetic data of the dissolution were obtained at microelectrodes by using the advantage of extracting kinetics from diffusion currents. Voltammetric currents at microelectrodes were smaller by 10 times than those predicted from diffusion of hydrated hydrogen. Therefore, the oxidation is controlled by the dissolution rate at the high current density. The rate was estimated to be 2 Â 10 À8 mol s À1 cm À2 , which was converted to the linear transfer rate, 0.4 mm s À1 , at gas|water interface.
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