The preparation and photoelectrochemical properties of various kinds of size-quantized semiconductor (Q-Sc) nanoparticles are described. The charge transfer across the Q-Sc particles is quantitatively discussed in terms of the size quantization and the effects of the surface modifiers on Q-Sc. Finally a novel technique of photoetching of Q-CdS particles is described as an effective means of the preparation of monodisperse Q-CdS particles.
The cathodic current density for CdTe electrodeposition from ammoniacal alkaline baths (pH 10.7∼10.8) was enhanced by photo-irradiation of the cathode surface. Voltammetric analysis revealed that the photo-induced enhancement was caused by CdTe deposit on the growing surface. By this irradiation, deviation of the composition of the resulting CdTe film from stoichiometry was depressed and current efficiency increased. The photo-assisted growth was discussed in terms of the deposition mechanism.
Direct internal CO2 reforming of methane was carried out on the anode of a planar solid oxide fuel cell (SOFC), which was composed of Ni-yttria-stabilized zirconia (YSZ)/YSZ/La0.6Sr0.4MnO3. I-V characteristics of SOFC were found to be basically similar to those obtained in internal steam reforming of methane. At CO2/CR4 =2.6 or higher, a stable voltage output was obtained without coke formation. The equilibrium open circuit voltage (OCV) for steam reforming of methane was expected to be slightly higher than that for CO2 reforming of methane at the same ratio of CO2/CR4 and H2O/CH4, whereas higher OCV was observed for CO2 reforming than for steam reforming of methane. The reason should be ascribed to the non-equilibrium states of the reaction gas mixture due to deficient amount of the Ni catalyst. CO2 reforming of methane is another suitable way to generate electrical power from methane fueled SOFC.
The purpose of this work is to elucidate whether or not the electrostatic interaction between the cathode and the suspended particle dominates the codeposition behavior. Barium sulfate particle was used as dispersed particle, because its surface charge development reaction is simpler than that of the oxide particle. In order to know the charged state of the particle in the bath, the ζ-potential of the particle was determined by a streaming potential method. It was clarified that there is no relation between the codeposition behavior of the particle and the charged state of the particle, although the latter may affect the quantity of the codepositing particle. It was suggested that the presence of the depositing metal ion on the particle is important for the codeposition behavior, irrespective of the sign of the charged state of the particle.
The relation between the codeposition behavior of the particle and the pH shift near the cathode according to hydrogen evolution was studied. A Watts type bath with α-alumina particle was used for the investigation. In order to elucidate the effect of pH shift on the metal ion adsorption, potentiometric titration was performed. It was clarified that the pH plateau of the titration curve for nickel sulfate solution in the presence of α-alumina particle is less than the pH plateau of the titration curve without α-alumina particle. This means that nickel ion is fixed on the surface of the oxide nevertheless hydroxide production does not occur in the bulk, at a certain pH. In this condition, the fixed nickel ion on the particle is able to induce the codeposition of the particle.
Light emission from the metal electrodes cathodically polarized at cell voltages up to 250 V was investigated in various aqueous electrolyte solutions. The light emission was observed when the temperature of electrodes exceeded the boiling temperature of the electrolyte due to the intense cathodic polarization: a thin vapor layer was formed at the metal/electrolyte interface in which a high electric field ionized vapor molecules to generate the plasma state. The light emission was caused by a glow discharge at relatively low cell voltages and by a spark discharge at high cell voltages. The spectra of the emitted light were assigned to the constituents of the electrolyte solution, electrode material and gaseous hydrogen evolved at the electrode.
Electrosynthesis of squaric acid was accomplished under low CO pressure (ca. 10 kgf cm−2). CO was reduced to squarium ions in an electrolyte consisting of THF-DMF mixture with 0.1 M tetra-n-butylammonium bromide. Current efficiencies for squaric acid formation were examined at Fe, Zn, Al, Ti, Ni and stainless steel (SUS304, SUS316, SUS321, SUS347 and SUS430). The current efficiency for squaric acid formation is about 45% at less than 15 mA cm−2 at SUS430 cathode, and decreases at more than 10 mA cm−2 at Mg anode. The formation of squarium ions needs at least 10 kgf cm−2 CO pressure. Squarium ions are hardly formed in an electrolyte containing 1% water.
Surface treatment of LiMn2O4 powder as a cathode material for lithium ion battery was done using the reaction that AgNO3 decomposes to Ag at high temperature. The surface characteristics were studied by means of a TEM and a potentiometric titrator. The charge-discharge performances of the LiMn2O4 powder were tested at a constant current density of 0.50 mA cm−2, and at 30°C and 60°C. The results showed that the surface treatment can significantly improve the charge-discharge performance.
To evaluate the effects of H2S on the performance of MCFC, the bench-scale cell tests and the half-cell tests were performed with fuel gas containing several levels of H2S. The behaviors of sulfur compounds in the cell depend on the absorption of S on anode Ni and the solubility of H2S by electrolyte. The solubility of H2S by electrolyte relates to partial pressure of gas composition according to H2S+CO32−+3H2O=CO2+4H2+SO42− and the current density. The higher the current density is, the lower the content of sulfate and / or sulfide ion in electrolyte is. Because the distribution of sulfate and / or sulfide ion depends on the convection of carbonate ion. In addition, the diffusion coefficients of sulfur in molten carbonate mixtures are derived from the bench-scale cell tests and the half-cell tests. The difference of these diffusion coefficients is discussed.
In order to improve the durability of phosphoric acid fuel cells (PAFC), it is essential to suppress the corrosion rate of carbon, which is one of the important components. In this study, we examined the influence of the orientation of carbon fibers on their corrosion rate in hot phosphoric acid. Owing to their ability to cover the surface of the graphite basal plane and thereby reducing the active site, onion-like folded carbon fibers were found more stable in hot phosphoric acid than radial folded carbon fibers, given the same degree of graphitization.
The membrane potentials of γ-MnO2 and Mn3O4, which were electrochemically prepared on Pt mesh, were measured in neutral aqueous solutions of KCl, KNO3, NaCl and Na2SO4 at 25°C to examine the transport numbers of the electrolyte ions in the Mn oxides. In these solutions, the cation transport numbers, t+, in γ-MnO2 were 0.62∼0.73, which were larger than those (0.38∼0.51) in the bulk solutions. On the other hand, the anion transport numbers, t–, in Mn3O4 were 0.62∼0.79, which were larger than those (0.49∼0.62) in the bulk solutions. The above results indicated that γ-MnO2 was cation-selective, whereas Mn3O4 was anion-selective. The difference in selective ion permeability between γ-MnO2 and Mn3O4 was explained in terms of the difference in sign of surface electric charge, depending on zero point of charge (zpc) of Mn oxides and pH of the used solutions.