An attempt has been made to prepare γ-alumina containing nickel in framework by a solution process, and to apply the nickel-containing alumina for filler in polymer electrolyte based on poly(ethylene oxide). The obtained polymer electrolyte exhibits higher conductivity than those without filler and with alumina filler in particular at temperature lower than 45°C, while the mobility of lithium ion appears to be similar regardless of the existence of nickel in alumina filler. This attempt has exhibited that the ceramic particles containing transition metal species can be used as effective fillers for the improvement of transport properties of polymer electrolytes.

View full abstract

The sintering behavior of (Sr_0.9La_0.1)_1−xTi_1−yO_3+δ powders (x, y=0, 0.04), synthesized using the Pechini method, has been investigated. Stoichiometric (Sr_0.9La_0.1)TiO_3+δ showed a single perovskite phase. For non-stoichiometric samples, secondary TiO₂ and Sr₂TiO₄ phases were observed in the X-ray diffraction patterns of (Sr_0.9La_0.1)_0.96TiO_3+δ and (Sr_0.9La_0.1)Ti_0.96O_3+δ, respectively. It was found that during the sintering process, the (Sr_0.9La_0.1)_0.96TiO_3+δ and (Sr_0.9La_0.1)TiO_3+δ samples expanded anomalously between 1300°C and 1400°C and between 1400°C and 1500°C, respectively, although the powders exhibited good sinterability. Scanning electron microscopy showed that the volume expansion was caused by pore formation within the samples. The release of oxygen from the samples was observed at temperatures at which the samples expanded and is considered to be the likely cause of the expansion.

View full abstract

Electric conductivities of PbWO₄- and PbMoO₄-based oxide ion conductors have been measured in the reducing atmospheres to investigate the transport properties and to evaluate the applicability to the solid electrolytes of fuel cells. Although almost all the solid solutions showed conductivity enhancements due to appearance of n-type electronic conduction with decreasing P_O2 down to 10⁻¹² atm, pure oxide ion conduction was maintained in the measured P_O2 range of ∼10⁻¹⁸ atm at 900°C only for Pb_1−xLa_xWO_4+x/2 system. For the tungstate and molybdate mixed crystal systems, furthermore, electronic contribution appears at higher P_O2 with increasing molybdenum content. Comparing the two types of substitutions, i.e. Pb_1−xLa_xMO_4+x/2 and Pb_1−xLa_2x/3MO₄ systems (M=W, Mo and mixed one), the former system tended to keep oxide ions in lattice rather than the latter, whereas the former contains excess oxide ions at the interstitial sites. At the end of this paper, test fuel cells have been constructed using Pb_1−xLa_xWO_4+x/2 solid electrolyte and operated at 500°C employing wet CH₄ gas as the fuel.

View full abstract

Reaction mechanism during the mechanical milling synthesis of sulfide based solid electrolytes in the system Li₂S-P₂S₅ was investigated in order to develop a speedy preparation process of the solid electrolytes. The sample preparation by using only milling process without heat treatment did not cause the increase in ion conductivity of the samples. On the other hand, the preparation process by using not only the milling but also heat treatments at a temperature around 210°C resulted in the increasing of lithium ion conductivity of the samples. This result suggested that the milling process combined with the heat treatment was very effective to prepare the amorphous samples in the system Li₂S-P₂S₅ with high ion conductivity.

View full abstract