Keisuke Hatakeyama

Visualization of hydrogen in hydrogen storage alloys using neutron radiography

Abstract Small amounts of hydrogen in hydrogen storage alloys, such as Mg2Ni, were detected using neutron radiography (NRG). Hydrogen concentrations in a hydrogenated solid solution were determined by this technique. Furthermore, we were able to obtain NRG images for an initial stage of hydrogen absorption in the hydrogen storage alloys. NRG would be a new method of measurement to clarify the behavior of hydrogen in hydrogen storage alloys.

Analysis of hydrogen distribution in hydrogen storage alloy using neutron radiography

Abstract The initial stage of hydrogen absorption was investigated on Mg–Ni based alloys, such as Mg2Ni and Mg3Ni (the eutectic mixture of Mg2Ni and Mg), using neutron radiography (NRG). The NRG images were obtained by not only a simple transmission method but also a tomographic one, which could clearly visualize hydrogen distribution in the alloys. The hydrogen diffusion coefficient in these alloys was estimated to be ≈2×10−7 cm2 s−1 from the change in hydrogen absorption depth with hydrogenation time. The comparison of the volume expansion rate due to hydrogen absorption for the alloys showed that Mg3Ni has better toughness than Mg2Ni until Mg3Ni was partly degraded to form magnesium hydride. Thus, NRG was found to be a powerful tool to clarify the behavior of hydrogen in hydrogen storage alloys.

Hydrogenation characteristics of the proton conducting oxide–hydrogen storage alloy composite

Hydrogen absorption–desorption characteristics of a proton conducting oxide, SrCe0.95Yb0.05O3−δ, were investigated using an electrochemical technique for the first time. It is suggested that the oxide can electrochemically repeat hydrogen absorption and desorption like hydrogen storage alloys. Subsequently, we attempted to improve activation properties of a hydrogen storage alloy, MmNi3.72Co0.60Mn0.45Al0.32, by mixing the proton conducting oxide. As a result, the oxide–alloy composite was found to enhance the activation performance of anode in Ni–metal hydride battery. The proton conducting oxide lying on the surface corrosion layer of alloy particles plays a role as a new path for hydrogen atoms to go into the alloy.

Solid-state metal hydride batteries using ZrO2·nH2O as an electrolyte

ZrO2·1.5H2O or ZrO2·1.5H2O-KOH composite was used as an electrolyte in order to develop a solid-state nickel-metal hydride battery. The battery using the ZrO2·1.5H2O-KOH composite had rechargeability, but had a very low discharge efficiency, even at low current density. However, the performance of the battery was prominently improved by enlarging the electrode-electrolyte interface area. The resultant battery exhibited the remarkably longer cycle life, the higher discharge efficiency, and the lower polarization: it was able to operate over 150 cycles at 10 mA/g alloy.

Solid-state metal hydride secondary batteries using heteropolyacid hydrate as an electrolyte

In order to enhance the performance of a solid-state MnO2-metal hydride battery using H3PMo12O40 · 20H2O as an electrolyte, a moderate amount of the electrolyte was added to both positive and negative electrodes. The high rate characteristics of the battery were improved significantly by optimizing the electrolyte content in the electrodes; the resulting battery was able to operate over 140 cycles, even at a current density of 20 mA/g alloy, which is large enough for the batteries using inorganic solid electrolytes, and keep the discharge efficiency about 90%. The improvement of battery performance appears to be caused by an increase in electrode-electrolyte interface area. The AC impedance analyses revealed that the resistance of interface is decreased by the addition of a suitable amount of the electrolyte, suggesting an increase in the interface area.