Kinetic improvement of hydrogen storage alloy by generating nanofissures

Hydrogen storage alloys are attracting worldwide attention as hydrogen suppliers to fuel cells. However, several kinetic problems remain to be solved before practical use is possible. A methodology to accelerate reactions of hydrogenation and dehydrogenation and to lower the reaction temperature is strongly required. In this study, therefore, to overcome these problems, a production method based on hydriding combustion synthesis (HCS) was applied to produce a metallic hydride directly and the kinetics of the product was microscopically studied and compared to the commercially available product based on ingot metallurgy (IM). The results showed that the HCS product was fully charged by hydrogen in the form of Mg2NiH4 just after synthesis and had a very large reaction rate with no activation treatment; only 5 min for full charge. A most interesting result is the high activity of our product: it stored hydrogen even at room temperature. Moreover, transmission electron microscopy (TEM) observation revealed the mechanism of the improved kinetics of the HCS product. Many tree-like nanofissures emerged inside the HCS product just after the first dehydrogenation; in contrast the IM product has no fissures even after three times activation treatment. In conclusion, a methodology has been introduced to improve a hydrogen storage alloy kinetically by generating nanofissures from inside, not from the surface, which could be applied to other hydrogen storage alloys. (C) 2003 The Electrochemical Society.