Nanotechnological APPROACHES IN THE DEVELOPMENT OF Materials for Hydrogen Storage
Actual developments in the field of hydrogen storage mainly deal with the development of materials based on the principles of chemisorption (metal hydrides in general) and physisorption. A nanotechnological approach has turned out to be highly beneficial in this field.
Complex aluminum hydrides, the so-called alanates, are chemisorption materials with high gravimetric storage densities for hydrogen. It will be shown that their dehydrogenation temperature depends on the grain size and that the kinetics of decomposition and hydrogen uptake are governed by nucleation and growth of the new phases [1,2]. Kinetic data suggest that diffusion processes in the solid limit the rate of their rehydrogenation. Hence, shortening of diffusion paths would be necessary to enhance the kinetics, e.g. by reduction of the grain size of the dehydrogenated material.
Kinetic barriers interfere with the hydrogen uptake and release and it has been tried to reduce the barriers by using appropriate dopants. In various studies Ti turned out to be the most active element for the process. It will be shown that a nanocomposite consisting of sodium alanate (NaAlH4) and a catalytic amount of small ligand stabilized Ti clusters (Ti13) shows considerably increased exchange rates for H when compared to a state-of-the-art catalyst.
Nanoscale physisorption materials have regained importance after a new class of nanomaterials with very high specific surface areas has been tested for hydrogen storage. Microporous isoreticular metal-organic frameworks (IR-MOFs)  seem to have the potential to store several weight% of hydrogen at room temperature and moderate pressures. In order to optimize these structures, theoretical investigations have been made  and results of a work will be shown about the binding energy of molecular hydrogen interacting with various (substituted) aromatic hydrocarbons.
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