Processes are provided for the storage and release of
hydrogen by means of a substantially reversible
catalytic hydrogenation of extended pi-conjugated substrates which include large polycyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons with
nitrogen heteroatoms, polycyclic aromatic hydrocarbons with
oxygen heteroatoms, polycyclic aromatic hydrocarbons with
alkyl, alkoxy,
ketone,
ether or polyether substituents, pi-conjugated molecules comprising 5 membered rings, pi-conjugated molecules comprising six and five membered rings with
nitrogen or
oxygen hetero atoms, and extended pi-conjugated organic polymers. The
hydrogen, contained in the at least partially hydrogenated form of the extended pi-
conjugated system, can be facilely released for use by a catalytic
dehydrogenation of the latter in the presence of a
dehydrogenation catalyst which can be effected by lowering the
hydrogen gas pressure, generally to pressures greater than 0.1 bar or raising the temperature to less than 250° C. or less, or by a combination of these two process parameters.