Hydrogen in V-Fe thin films and Fe/V-Fe multi-layered thin films

Ever since the energy crisis in 1970¿s, hydrogen (H) has been regarded

as one of the carbon-free secondary energy sources. In this context, hydrogen

storage materials have been considered as possible candidates of

clean energy storage media (see e.g. website of Department of Energy in

US [DOE]). Hydrogen is the smallest and the lightest element and thus

can be easily absorbed in interstitial sites of metal lattice. A pioneering

work in this field is known by Sieverts [Siev29]. In some of metal alloys

with tailored composition, considerable amount of hydrogen (several wt%)

can be reversibly stored through metal/metal hydride (MH) phase transition,

just by controlling pressure or temperature [Vught70]. Practically,

some of them (LaNi5, TiFe) are really easy to handle and have already

been utilized for technical applications like in fuel cell system [Iwas03] or

in MH refrigerator [Uchi04] after intensive studies and developments in

this field. Owing to its extraordinary high volume density and high stability,

such metal hydrides still hold advantage to other storage methods

like liquid hydrogen or high-pressure H2 gas tanks. Currently, further research

and development is on the way focusing on improvement of gravimetric

hydrogen density and reaction kinetics [Orimo07, Dornh07].