Reona Miyazaki

Synthesis of rock-salt type lithium borohydride and its peculiar Li+ ion conduction properties

The high energy density and excellent cycle performance of lithium ion batteries makes them superior to all other secondary batteries and explains why they are widely used in portable devices. However, because organic liquid electrolytes have a higher operating voltage than aqueous solution, they are used in lithium ion batteries. This comes with the risk of fire due to their flammability. Solid electrolytes are being investigated to find an alternative to organic liquid. However, the nature of the solid-solid point contact at the interface between the electrolyte and electrode or between the electrolyte grains is such that high power density has proven difficult to attain. We develop a new method for the fabrication of a solid electrolyte using LiBH4, known for its super Li+ ion conduction without any grain boundary contribution. The modifications to the conduction pathway achieved by stabilizing the high pressure form of this material provided a new structure with some LiBH4, more suitable to the high r...

Cobalt Doping as the Controlling Factor of Oxygen Diffusivity in ZnO by More than Four Orders of Magnitude

Oxygen diffusivity in ZnO ceramics doped with cobalt was investigated using an isotope tracer method. The oxygen isotope (18O) was introduced by 18O/16O exchange annealing in an 18O2 atmosphere, and the depth profile of the 18O concentration was analyzed by secondary ion mass spectrometry. The results show that oxygen diffusivity in ZnO steeply increases with increasing Co concentration. In fact, the bulk oxygen diffusivity in 15 mol% Co-doped ZnO was four orders of magnitude greater than that of nominally non-doped ZnO. Oxygen diffusivity at grain boundaries was also enhanced by Co-doping.

PEFC catalytic properties of Pt – Ni nanoparticles prepared by a plasma-gas-condensation

Pt – Ni nanoparticles were fabricated via the gas phase method. Their performance as anode catalysts for the proton exchange membrane fuel cell was investigated as a function of Ni concentration. The microscopic configurations of the nanoparticles were rather heterogeneous; Pt-rich alloys existed in the core region of particles while a part of the surface layer was composed of the Ni-rich layer. Despite the Ni-rich layer in the shell region, the anode catalyst performance of the Pt – Ni nanoparticles was never deteriorated compared with that of the Pt ones. When the anode catalyst was composed of the Pt nanoparticles, a maximum power density of 112 mW/cm2 was obtained. However, 90% of the power density was still kept even when 40 at. % of Pt was replaced with Ni. The results suggest that a further decrease of Pt composition with maintaining its catalyst performance can be feasible by effective particle dispersing.