NOVELTY - Repeatable dehydrogenation process (M1) involves introducing liquid comprising at least one conformer of at least partially hydrogenated pi-conjugated compound into environment containing at least one catalyst under conditions to dehydrogenate at least portion of the compound. The compound comprises at least one member selected from extended pi-conjugated substrates with a heteroatom, extended pi-conjugated substrates with greater than 3 rings and extended pi-conjugated substrates with at least 2 rings, where one ring is 5 membered ring, and is repeatedly hydrogenated and dehydrogenated.    USE - For releasing and subsequent storing of hydrogen (claimed), particularly for supplying hydrogen to fuel cells.    ADVANTAGE - The process is a reversible hydrogenation of pi-conjugated substrates to provide for the storage and release of hydrogen at practical operating temperatures and pressures, particularly for supplying hydrogen to fuel cells. The pi-conjugated substrates are reversibly catalytically hydrogenated at milder reaction conditions and with a lesser expenditure of energy than those of the prior art, i.e. principally benzene, toluene and naphthalene. The extended pi-conjugated substrates is that they and their hydrogenated derivatives are far less volatile, thus precluding the need for a separate unit operation for totally separating these from the product hydrogen thus greatly simplifying the overall hydrogen storage equipment and its process of operation.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) producing (M2) hydrogen involving either: contacting at least one at least partially hydrogenated extended pi-conjugated substrate with at least one catalyst under conditions to produce a hydrogen containing product, where the substrate comprises the at least one conformer, and is capable of being at least partially hydrogenated subsequent to the contacting; or heating a liquid comprising at least one, at least partially hydrogenated pi-conjugated substrate having at least one heteroatom and at least one conformer of the substrate, and at least one catalyst to produce hydrogen gas and at least one liquid de-hydrogenated substrate; separating hydrogen gas from the at least one liquid de-hydrogenated substrate, where the de-hydrogenated substrate is less volatile than hydrogen and is hydrogenated; and recovering hydrogen gas;    (2) releasing (M3) hydrogen involving either: exposing a liquid comprising at least one at least partially hydrogenated pi-conjugated compound with at least one catalyst under conditions to remove hydrogen from the liquid to produce a hydrogen containing fluid, where the compound comprises the at least one conformer, and the process is substantially free of solvents, and hydrogen is reintroduced and subsequently removed from the compound; or exposing a liquid comprising at least one non-equilibrium conformer, of at least one, at least partially hydrogenated compound with at least one catalyst under conditions to remove hydrogen from the liquid to produce a hydrogen containing fluid;    (3) storing (M4) hydrogen involving: exposing a liquid comprising at least one non-equilibrium conformer with at least one catalyst under conditions to hydrogenate a least a portion of the liquid.