Manabu Tanaka

Phosphoric acid-doped sulfonated polyimide and polybenzimidazole blend membranes: high proton transport at wide temperatures under low humidity conditions due to new proton transport pathways

We now demonstrate a new class of a polymer proton exchange membrane for fuel cells, capable of combining low cost and high proton conductivity under low humidity conditions. The novel phosphoric acid (PA)-doped sulfonated polyimide (SPI) and polybenzimidazole (PBI) blend membrane enables proton conductivities of approximately 0.5 and 0.1 S cm−1 at 120 °C and 45%RH and at 30 °C and 30%RH, respectively. These conductivities were approximately two orders of magnitude higher than those of Nafion 117 due to a new proton transport pathway between phosphoric acid and sulfonic acid in the blend membrane. In addition, the membrane showed no signs of performance degradation at 120 °C and 0%RH after 1000 hours of operation, and maintained a proton conductivity value of more than 0.01 S cm−1. Consequently, this material shows promise as a novel proton exchange membrane and may have potential applications for use in fuel cells.

Porphyrin-Containing Electrospun Nanofibers: Positional Control of Porphyrin Molecules in Nanofibers and Their Catalytic Application

Polyacrylonitrile nanofibers containing a series of porphyrin molecules were prepared by an electrospinning method. We first succeeded in controlling the position of porphyrin molecules in the nanofibers by considering porphyrin characteristics and the electrospinning conditions. It was concluded that positive charge of cationic porphyrin, TMPyP, and higher applied voltages were effective to locate the porphyrin molecules on the polymer nanofiber surfaces because of the electrostatic repulsion among the molecules during the electrospinning process. The polymer nanofibers with cationic manganese-porphyrin (Mn-TMPyP) on their surface repeatedly showed superoxide dismutase (SOD) activity, which is a catalytic activity to work as antioxidant in various biochemical fields. The positional control of functional molecules in nanofibers demonstrated a new possibility of nanofiber applications.

Ultra-high proton conduction in electrospun sulfonated polyimide nanofibers

Uniaxially-aligned sulfonated polyimide (SPI) nanofibers fabricated by an electrospinning method showed ultra-high proton conductivities above 1 S cm−1 at 30–90 °C and 95% RH. Higher applied voltage between the parallel electrodes during the electrospinning process gave higher proton conductive SPI nanofibers due to the formation of an effective proton conduction pathway by molecular orientation in the nanofibers.

Fabrication and electrolyte characterization of uniaxially-aligned anion conductive polymer nanofibers

We report the anion transport properties of anion conductive polymer nanofibers fabricated using an electrospinning method. The aligned nanofibers were prepared to evaluate the anion conductivity of the nanofibers. The aligned nanofibers had 10-15 times higher conductivity (up to 160 mS cm-1 at 90 °C and 95%RH) and lower activation energy (23-25 kJ mol-1) than the corresponding membranes, even though the nanofibers showed lower water uptake than the corresponding membranes. The anion conductivity measurement of nanofibers with different IEC values and anion species revealed that the dependency of anion conductivity on these factors was smaller in the nanofibers than in the corresponding membranes. These results indicate that effective ion transport pathways were formed in the nanofibers due to the phase separation and the polymer chain orientation along the nanofiber axis. These nanofibers are expected to be useful for future applications in alkaline fuel cells, air batteries, and other energy- and environment-related devices regardless of the ion species.

The deformation and fracture of austenitic heat-resisting steel with grain-boundary reaction nodules

The tensile properties in 21-4N austenitic engine valve steel containing pearlitic nodules due to the grain-boundary reaction have been investigated at room temperature. Some theoretical considerations on the deformation and fracture behaviour of this steel are also presented. In the steel with grain-boundary reaction nodules more than about 10% in area fraction, the ductility decreases considerably with their increase owing to the brittle fracture of rod-like precipitates in the nodules. Although the grain-boundary reaction also decreases the tensile stress and 0.2% proof stress, its effect is more noticeable on ductility than on strength. A theory is developed to explain the workhardening behaviour as well as the fracture mechanism using a model for composite materials and a good agreement between theoretical and experimental results is obtained.

High Temperature Deformation of Materials with Precipitates : Temperature and Particle Size Dependence of Work Hardening Behavior

The temperature and particle size dependence of work hardening of metallic materials with second phase particles at elevated temperatures, where the dynamic recovery by volume diffusion of atoms is dominant, has been calculated on the basis of a continuum mechanics model without any ambiguous parameters. It was confirmed that there was a good agreement between the result of calculation based on this model and the one of tensile test in an austenitic heat-resisting steel with M23C6 carbides. Further, the model in this work was also applied to the interpretation of the internal stress during steady-state creep in this steel.