Therefore, hydrogen is being widely discussed as a future energy source to replace hydrocarbons. However, there is no practically viable storage process for hydrogen the horizon, in particular for its use in vehicles powered by fuel cells in which the hydrogen must be stored in as small a volume and as low a weight as possible. A 700 bar pressure accumulator is currently the most highly developed hydrogen storage option. Liquid hydrogen storage systems have also been used in fuel cell vehicle prototypes. For various reasons, however, neither of these processes is truly satisfactory.
Interestingly, hydrogen can be packaged even more compactly in certain compounds from the metal hydride family than in liquid form. If hydrides can be found that absorb hydrogen in the required temperature range at high pressure and release it again at low pressure, this could provide a basis for the resolution of the storage problem. Research on this approach is currently being developed at the Max Planck Institut für Kohlenforschung - however, the starting point of this work was basic research carried out as far back as the 1970s.
The particular focus of interest here was the homogenous catalytic production of metals. When extended to other hydrides and mixed systems, it was found that there is a huge increase in the hydration and dehydration rates of sodium aluminium when small volumes of other metals are added. Titanium was identified as the most effective element in these early studies. It is only by increasing the reaction rate through the use of such a catalyst that these systems could, in principle, be used in cars, as this would enable sufficiently rapid refuelling. Further research has allowed other catalysts to be, some of which display better characteristics than the titanium originally used. The way in which the catalysts work is now also understood in part. The sodium aluminium hydride system is currently among the best available hydrogen storage materials; however, the storage capacity it offers is still too low for use in cars. Therefore, based on these studies, other metal systems have been researched in cooperation with Opel/GM Fuel Cell Activities with a view to discovering other more efficient hydride systems. Although the long-term objective of this research is to develop hydrogen storage systems that are suitable for use in practice, it is characteristically very basic, as little work has been done up until now to investigate the material systems and some new synthesis pathways still need to be explored.