The perovskite type oxides, Lnl-xAxM03-δ (Ln = lanthanides, A=Sr, Ca, M=Mn, Co), were studied as cathode materials in solid oxide fuel cells (SOFC) from a view point of compatibility with the solid electrolyte of yttria stabilized zirconia (8 mol% Y203 doped zirconia, 8YSZ). Generally, the pyrochlore, La2Zr2O7, can form at the boundary between the perovskite and 8YSZ. In the case of Lnl-xSrxMnO3-δ (Ln=La, Pr, Nd, Sm, and Gd), the formation of the pyrochlore, Ln2Zr2O7, was suppressed for the perovskites having smaller lanthanoids than La, especially for the Prl-xSrxMnO3-δ and Ndl-xSrxMnO3-δ systems. The Lnl-xAxCoO3-δ systems with samaller lanthanoid ions were also effective in suppressing the reaction with 8YSZ. However, the Lnl-xAxCoO3-δ systems, which are promising cathode materials for a low operating temperature SOFC, have larger thermal expansion rates than 8YSZ. The formation of a solid solution with Mn in the B-site of the perovskite such as Gdl-xAxMn1-y COyO3-δ (A = Sr and Ca) brought reasonable thermal expansion rates, compatible with 8YSZ and high oxygen reduction catalytic activity.
The cyclic-magnetammetry (CM) to analyze electrochemical reactions in a magnetic field has been newly proposed; a periodically changing magnetic field is applied to a magnetohydrodynamic electrode (MHDE) in a vessel filled with an electrolyte solution. During the electrolysis under potentiostatic condition, current response is measured against magnetic flux density. Using the locus of the current against the magnetic flux density (the cyclic magnetarnmogram), we can examine the special magnetic field effects on the reaction and diffusion processes excluding the usual MHD effect. Experiments were carried out for redox reactions between ferricyarLide and ferrocyanide, and copper reduction in sulfuric acid. It turned out that, in the former redox reaction, the locus converged to a straight line as expected. However, in the copper reduction, obvious hysteresis effect on magnetic field and periodic current response were observed.
It is well known that the amount of physisorbed water molecules decreases by thermal and evacuating treatments at anatase TiO2 surfaces.1-3) However, the initial water contact angle of the anatase TiO2 surface coated on the glass was little changed (from 24° ± 1° to 23° ± 1°) and the hydrophilicity did not change by the heating treatment at 150°C for 1 hour. On the other hand, the value of its initial contact angle increased remarkably (from 24° ± 1° to 67° ± 1 0), and the TiO2 surface was hydrophobicized by the evacuation at ~5 × 10-6 Pa. These observations may show that not only the amount of physisorbed water molecules but also the structure, i.e., OH groups of TiO2 surfaces are related to the hydrophilicity. The photo-decreasing rate of the water contact angle under the ultra violet (UV) illumination at the anatase TiO2 surface (the photo-induced hydrophilic conversion rate) increased by the heating treatment at 150°C for 1 hour. However, photo-induced hydrophilic conversion rates were little changed by the evacuating treatment at ~5 × 10-6 Pa. These results suggest that the photo-induced hydrophilic conversion phenomena are not necessarily affected by the initial amount of physisorbed water molecules.
Polarization curves of iridium oxide-coated titanium electrodes used for oxygen evolution and chlorine production prepared by a range of electrochemical methods were evaluated in H2SO4 and NaCI solutions. Although the iridium oxide-coated electrode prepared by DC plating of iridium on Ti followed by electrolytic oxidation in NaCI solution using a rectangular wave showed the lowest overpotential for oxygen and chlorine electrode, the lifetime was short. The iridium oxide covered titanium electrode plated using a triangular wave showed the second best catalytic activity and longer lifetime. The surface of these two electrodes was found to be covered by iridium hydroxide and water. By heating the triangular wave electrode at 450°C in air, the lifetime was increased and exceeded that of the electrode prepared by conventional thermal decomposition method without a significant decrease in catalytic activity.
The influence of curing process has been studied to measure trickle-charging current during trickle use for a sealed-lead acid battery. The investigation has been studied to measure pore distribution for active material and to analyze impedance measurement for negative electrode. According to trickle charging evaluation test for a cell, trickle-charging current depended on the curing temperature and humidity. Pore distribution measurements for active materials showed that surface area of active material depends on curing temperature. Curing at 75°C showed much trickle-charging current. From the impedance analysis, it was shown that the reaction resistance for lead on surface of the electrode changed with the curing temperature and humidity. As to reduce trickle-charging current, it means to tend not to be polarized, there was the suitable condition in curing process around 56-65°C and 0.12-0.16 H2O kg dry air−1.
In case of operating a polymer electrolyte fuel cell (PEFC) with Pt-Ru alloy for the anode catalyst at low temperature, oscillation phenomena of the cell voltages are often observed. In order to study the phenomenon with CO poisoning in PEFCs, we used a “divided cell”. In the “divided cell” which consisted of two single cells, fuel gas was supplied in series from the “upstream cell” to the “downstream cell”. Air was supplied in parallel to the both cells. An electric load was also connected in parallel. When fuel changed from pure hydrogen to CO containing gas, the current at the upstream cell decreased and that at the downstream cell increased. This result indicates that the CO poisoning occurred mainly in the upstream cell. In general, oscillations of the cell voltages were observed under low operation temperature (ex. below 60°C) or CO-rich conditions. When the voltage oscillates, the current density of each cell in the divided cell also oscillates synchronized with the voltage oscillation. In all cases, CO concentration of fuel exhaust gas was lower than that of fuel inlet gas. These results indicate that the oxidation reaction of CO with water occurs in the anode of the PEFC. The ratio of oxidized CO with water is proportional to CO concentration in the inlet fuel gas.
To obtain an orientation of design for highly functional film synthesized by electrocopolymerization, an attention was given to two copolymerization systems, that is, methyl acrylate (MeA)/acrylamide (AAm) and acrylic acid (AA)/acrylonitrile (AN) systems, having a different reactivity in radical copolymerization in solution system, the characterizations of films electrocopolymerized under various electrolytic conditions were evaluated. The MeN AAm film was able to be synthesized by electrocopolymerization and the composition was capable of controlling, The AN AN film was able to be electrocopolymerized but the control of composition was difficult. In particular, the composition of film was dependent on a reactivity of monomer rather than an electrolytic potential.