Masunobu Maeda

Photoelectrochemical reduction products of carbon dioxide at metal coated p-GaP photocathodes in non-aqueous electrolytes

Photoelectrochemical reduction of CO2 was carried out using metal-coated p-GaP photocathodes in non-aqueous electrolytes prepared from tetraalkylammonium salts and propylene carbonate as an aprotic solvent. In non-aqueous electrolytes, the coating of Au, In and Pb increased the cathodic photocurrents and the stability of the electrodes, while Zn coating did not show such significant effects. Photoelectrochemical reduction products at a bare p-GaP in non-aqueous electrolytes were (COOH)2, HCOOH, CO and H2, and the faradaic efficiency for CO formation became 50%, in contrast to that in the aqueous electrolytes where it was only a few %. The Photoelectrochemical reduction products at metal-coated p-GaP photocathodes depended greatly on the catalytic properties of the coated metal, i.e. the catalytic effect on the electrochemical reduction of CO2. By Pb coating, the faradaic efficiency for (COOH)2 formation became ca. 50%, and by Au, In or Zn coating, that for CO became almost 100%. The water content in non-aqueous electrolytes affected the faradaic efficiency of each product significantly.

Orientation control of zinc oxide films by pulsed current electrolysis

ZnO films were prepared on ITO/glass substrates by pulsed current electrolysis. The preferred orientation of the ZnO films was changed by varying pulse parameters such as the cathodic average current density and the pulse period. The change of the preferred orientation for ZnO films prepared by the pulsed current electrolysis agreed nearly with that predicted by the two-dimensional nucleus theory presented by Pangarov. It was suggested that the change of the preferred orientation of the ZnO films was caused by the effect of the pause of electrolysis in addition to that of the overvoltage. As a result, it was demonstrated that the preferred orientation of the ZnO thin films could be controlled by regulating pulse conditions for the pulsed current electrolysis.

Preparation of Zinc Oxide Thin Films by Pulsed Current Electrolysis

ZnO thin films were prepared on indium-tin oxide (ITO) substrates by pulsed current electrolysis. The preferred orientation of the ZnO thin films prepared by pulsed current electrolysis changed in order to (0002), (1011), and (1010) by the change in overvoltage. Green-yellow emission centered around 580 nm was observed for the ZnO films. The increase of intensity of the green-yellow emission may be ascribed to effects brought about during the pause of electrolysis. The transmittance at 600 nm for ZnO thin films prepared by pulsed current electrolysis was over 95%. It was demonstrated that pulsed current electrolysis is effective for control of preferred orientation and concentration of lattice defects and for improvement of the transmittance of ZnO thin films.

Porous glass-ceramics cation exchangers: Cation exchange properties of porous glass-ceramics with skeleton of fast Li ion-conducting LiTi 2 (PO 4 ) 3 crystal

Lithium titanium orthophosphate LiTi 2 (PO 4 ) 3 (LTP) has attracted attention as a chemically stable fast Li + -conductor in ambient atmosphere. It was reported in our previous paper 7 that monolithic microporous glass-ceramics with a skeleton of this crystal were successfully prepared from glasses in the pseudobinary system of LTP and Ca 3 (PO 4 ) 2 . Here we report that these porous glass-ceramics (mean pore diameter: ∼40 nm; total specific surface area: ∼30 m 2 ; porosity: ∼45 vol.%) show excellent cation exchange properties. Approximately 50% of Li + ions in the materials are exchanged with monovalent ions with ionic radii smaller than 130 ppm in 1 h at room temperature. In particular, Li + ions are selectively exchanged with Ag + ions even in the presence of Na + ions. The exchange rate in the porous glass-ceramics is larger by two orders of magnitude than that of sintered LTP. The ratio of these exchange rates is close to that of the total surface areas, indicating that most of the pores in porous LTP glass-ceramics are available for ion exchange reactions. These are the first porous glass-ceramics having excellent cation exchange properties.

Reduction of carbon dioxide on partially-immersed Au plate electrode and Au-SPE electrode

Abstract The electrocatalytic reduction of carbon dioxide was carried out on two types of Au plate electrode; one was partially immersed in electrolyte solution containing CO2 and the other was completely immersed. Their surface areas in contact with the solution were kept equal, so that the difference in Faradaic efficiency for the reduction of CO2 to CO between the two types of electrodes was examined. The effects of surface treatments of the electrodes and electrolytes on the Faradaic efficiency were also investigated for each type of electrode. When the electrode surface was treated by electroplating Au on the Au plate, the partially-immersed electrode brought about a higher Faradaic efficiency for CO2 reduction than the completely immersed one both in 1 mol dm−3 KHCO3 and in 0.1 mol dm−3 (C2H5)4NClO4 aqueous solution at room temperature. The Au-SPE (SPE: solid polymer electrolyte) electrode was applied as a gas diffusion electrode to the reduction of CO2, and the Faradaic efficiency for CO production was compared with that obtained by the partially-immersed Au plate electrode. The Au-SPE electrode gave rise to a higher Faradaic efficiency than the partially-immersed electrode.

Composition and geometry of oxovanadium(IV) and (V)-aminoethanol-Schiff base complexes and stability of their peroxo complexes in solution

Abstract Vanadium(IV) and (V) complexes (VO(sal-ae)) with Schiff bases prepared from 2-aminoethanol and salicylaldehyde and its derivatives have been synthesized and characterized in solid and in solution by EPR, IR, and UV–Vis spectroscopy. The complexes of both V(IV) and V(V) contain bridges (VOV) by alkoxy oxygens(oxo) in the solid state. The complexes of V(IV) in dichloromethane are binuclear,in which two alkoxy oxygens serve as bridges between the two metal atoms. They are mononuclear with one solvent ligated in the equatorial plane in each complex in dimethyl sulfoxide and methanol. The extent of the formation and the stability of organic hydroperoxide complexes of V(V) prepared from the V(IV)–Schiff base complexes increase with decreasing donor number of the solvent. The difference in electron-donating and withdrawing ability of the substituent groups affects the A‖ values for the V(IV)–Schiff base complexes in DMSO.

In situ Observation of the Crystallization Process of Ferroelectric Thin Films by Raman Microspectroscopy

Crystallization processes of ferroelectric strontium bismuth tantalate (SrBi2Ta2O9; SBT) films with a Bi-layered structure and lead zirconate titanate [Pb(Zr0.5Ti0.5)O3; PZT] films with a perovskite structure have been investigated by Raman microspectroscopy. Amorphous films were prepared by rf-magnetron sputtering at room temperature using nearly stoichiometric ceramic targets. In situ Raman observations were performed at intervals with increasing sample temperatures. Under a heating rate of 20°C/min, the SBT films began to crystallize at 710°C, and completed crystallization at 850°C. It was found that SBT film crystallization advanced rapidly in the temperature region from 750 to 800°C. Raman mapping measurements of the SBT films at room temperature after annealing at 700 and 800°C clearly indicated the nucleation and growth processes of the crystal grains, respectively. The Raman peaks of the PZT films, which were observed in situ in spite of the cubic symmetry at the annealing temperatures, showed perovskite structure formation at temperatures as low as 500°C.

Structure and electrical characteristics of Ce4+-doped Ba2In2O5

The In-site of Ba2In2O5 with Brownmillerite structure was partially substituted for Ce4+ ions in order to examine the doping effect on the order-disorder transition. Ba2In2 − xCexO5 + x/2 (x = 0.1, 0.2, 0.3, 0.5, 1.0, and 1.5) were prepared by solid state reaction. X-Ray diffraction analyses of these powder samples demonstrated that Ba2In2 − xCexO5 + x/2 (x = 0.1 and 0.2) possesses Brownmillerite structure. With increasing content of Ce4+ ion the crystal system of Ba2In2 − xCexO5 + x/2 (x = 0.3, 0.5, and 1.0) changed to cubic perovskite structure above the order-disorder transition temperature of Ba2In2O5. Arrhenius plots of the electrical conductivities of Ba2In2 − xCexO5 + x/2 (x = 0.2, 0.3, and 1.0) exhibited no discontinuity. These compounds had high transference numbers of oxide ion above 973 k.

The Hydrolysis of the Copper(II) Ion in Heavy Water

The hydrolysis of Be2+ ion in heavy water containing 3M NaClO4 as an ionic medium was investigated at 25°C by potentiometric titrations, employing a technique of constant-current coulometry. The deuterium-ion concentrations was measured by the use of a commercial glass electrode. The emf data in the range of the total beryllium concentration from 2.5 to 10 mM can be explained on the basis of the following complex formation: Be2(OD)3+, −logβ1,2=3.28±0.04; Be3(OD)33+, −logβ3,3=9.399±0.007; Be(OD)2, −logβ2,1=11.89±0.07. The composition of the species formed in heavy water is the same as that in light water, but the values of the stability constants are smaller in heavy water than in light water.

Origin of pH‐Glass Electrode Potentials and Development of pNa‐Responsive Glasses

Generally accepted theories about the origin of the pH response of glasses are based on the assumption that hydrogen ions do not cross the glass membrane. Based on our previous findings that there exist two types of hydrogen ions in glasses, one that is hydrogen bonded and mobile and the other is free of hydrogen bonding and substantially immobile, we proposed that the original presence of mobile hydrogen ions in glasses should be required for the glasses to exhibit the pH response. This proposition was experimentally proved. This indicates that any cations (M), if they are mobile in glasses, should show the pM response. The mobilities of the mobile hydrogen ions in pH-selective glasses were evaluated to be ca. 10 3 times higher than those of alkali ions.Thus, the essential condition for glasses to exhibit the pNa response should be that the mobility of hydrogen ions in the glasses should be kept as low as possible compared to that of Na + ions. This suggestion was experimentally verified for a 20Na 2 O-20Al 2 O 3 -60SiO 2 glass in which Na + ions are naturally mobile and H + ions are much less so.