Some of recent topics on the use of microelectrodes for the characterization of solid materials, especially the active materials of lithium ion batteries, were overviewed based mainly on our research. The microelectrodes used here can be classified to the microdisk and interdigitated array. The systems based on the microdisk electrodes were established for the characterization of a single particle of active materials. On the other hand, the interdigitated array microelectrodes were used for measuring conductivity changes of materials' film in situ during the lithium insertion / extraction reaction. It is demonstrated here that the microelectrode-based characterization techniques bring unique information, which will contribute to the design of high performance lithium ion batteries.
Interaction of some Lewis acids to the oxide bridge of [Ru2(μ-O)(μ-CH3COO)2(2,2'-bipyridine)2(L)2]2+ (L = 1-methylimidazole (1), pyridine (2)) and its electrochemical consequence were examined. The complexes themselves show reversible Ru2(III, III / III, IV) and Ru2(II, III / III, III) processes and an irreversible Ru2(II, II / II, III) process in acetonitrile (0.1 M n-Bu4NPF6) at 0.78 (0.95) (E1/2), −0.55 (−0.39) (E1/2) and −1.16 (−1.09) V (Epa) vs. Ag/ AgCl, respectively, for 1 (data in parentheses are for 2). On addition of BF3 and Al3+, all the redox potentials shift to the positive direction. Addition of Li+ and Na+ causes the shift of only the most negative El/2 to overlap with the middle one to show an apparent one-step two-electron process Ru2(II, II / III, III) at −0.55 V. BF3 and Al3+ interact with the oxide bridge of the complexes at the oxidation states Ru2 (III, III), (II, III) and (II, II) while the alkali metal ions do only at the Ru2(II, II) state.
Changes in the UV-Visible spectra of HCl-sorbed tetraphenylporphine (TPPH42+)-polymer composite films were examined for detection of ppm levels of HCl gas. On exposing the films to HCl gas, the following reversible reaction takes place; . Due to the formation of the dicationic form, the concentration of HCl gas was considered to be determined by the measurement of the absorbance changes. The sensitivity to HCl was discussed on the bases of the sorption models of Freundlich / Langmuir-type, clustering type and Henry's type. Freundlich / Langmuir-type sorption model was applied for the polymer with a higher glass transition temperature. Changes from Freundlich / Langmuir type sorption to clustering type sorption and then Henry's type sorption was observed with a decrease in the glass transition temperature.
Estimation of the overpotentials due to internal resistance, polarization by electrode reaction and Nernst Loss in Molten Carbonate Fuel Ce1l (MCFC) was mainly carried out by analyzing the variation of equilibrium output voltage fixed a current density under several gas conditions till now. On the other hand, transient response analysis methods such as AC Impedance and Current Interrupt are being applied to the estimation in bench-scale cell level for the last few years. In connection with the Current Interrupt measurement, the potential relaxation after current interruption is observed the internal resistance, the reaction polarization and Nernst Loss in order. The relaxation due to Nernst Loss is continued during10 sec range. The long time relaxation can not be explained from the values of gas velocity (10 cm/sec range) and gas phase diffusion（1 cm2/sec range） in a bench-scale cell (10×10 cm area). Therefore, we grasped the long time relaxation as the liquid phase diffusion process in electrolyte kept in porous electrode and estimated the apparent diffusion coefficients and diffusion layer in molten carbonate mixtures.
The initial deposition of electroless Ni-P films on gold electrodes modified with Pd ad-atoms was investigated using cyclic voltammetry and EQCM technique. It was found that the minimum coverage of Pd ad-atom catalysts is 0.01 for electroless Ni-P deposition. The initial deposition rates and the induction time for Ni-P plating are strongly influenced by the Pd coverage, and reached a maximum value at the coverage of 0.4. A maximum current density for H2PO2− oxidation was observed at the Pd coverage of 0.45, where H2PO2− adsorption is enhanced. The large amount of adsorbate of SO42− or HSO4−, which would inhibit H2PO2− oxidation at the initial deposition of electroless Ni-P films, was observed at the Pd coverage of 0.45 in H2SO4 solution.
An idea of a new electrochemical heat pump that uses the combination of an electrolytic reaction at lower temperature to absorb low grade thermal energy and a thermochemical reaction at higher temperature to produce more efficient thermal energy has been proposed. At lower temperature an endothermic reaction proceeds with electrolysis, where the reaction could not occur thermochemically. At higher temperature an exothermic reaction that is the reverse reaction of the electrolysis proceeds thermochemically to produce high grade thermal energy. The thermodynamic consideration showed that the theoretical coefficient of performance of this electrochemical heat pump with continuous transportation of working substances could reach up to the value of the inverse Carnot factor that is defined by the higher and the lower temperatures of the system. The irreversibility of the system such as the mechanical work required to transport of working substances and the thermochemical reaction at higher temperature decreased the coefficient. Introducing the quantity of the entropy production due to irreversibility, the relationship between the coefficient and the irreversibility was derived. The ΔH°‒ΔS° diagram (ΔH°: the standard enthalpy change of the reaction, ΔS°: the standard entropy change of the reaction) was found to be useful for the selection of the reactions.
A limiting current-type gas sensor was composed using a thin film of the high temperature type proton conductor, CaZr0.9In0.1O3-a. The perovskite structure film was obtained by sputtering in Ar and a heattreatment at 900°C in air. A hydrogen concentration cell with this film showed theoretical EMF's at the temperatures from 500°C to 700°C. Therefore this film was regarded as a proton conductor. The film also showed a conductivity of 7×10−5 S cm−1 at 700°C in hydrogen atmosphere. The limiting current type gas sensor was composed by laminating Pt films and the proton conductor film on a alumina porous substrate. The sensor showed limiting current characteristic corresponding to partial pressures of H2, C3H8 and CO. A linear relationship was obtained between the limiting current and partial pressure of these gases.
Catalytic film electrodes which were coated with poly [N -(5-hydroxypentyl) pyrrole] film and incorporated catalytic noble metals such as platinum, rhodium, and gold in the film were prepared. The order of incorporating amount in the film was gold, platinum, and rhodium. By use of these catalytic electrodes the electrochemical hydrogenation of methyl benzoylformate in an ethanol-HCl buffer solution was investigated. The hydrogenation on all catalytic electrodes provided methyl mandelate and the efficiency was good particularly on the electrode incorporating gold metal.
The mechanical alloying (MA) process of the oxide ion conductor (Bi2O3)0.80(Nb2O5)0.20 has been studied by means of X-ray diffraction, SEM observation and particle size measurements. The formation of the solid solution was supposed to proceed by flattening the sample powders into plate shapes and the repeated laminations as the case of the formation of metallic alloys. During milling, the crystallite size decreases down to 10 mm or smaller while the aggregated particle size was remaining about 1 μm.