The present invention relates to a composition capable of hydrogen sorption in a closed container at low pressure, comprising an unsaturated organic substance and a hydrogenation catalyst. Said unsaturated organic substance is a compound having general formula A or A′, or a dimer or polymer thereof, or a copolymer wherein one of the structural units has the general formula A or A′: wherein R1, R2 and R3 are hydrogen or hydrocarbon moieties optionally comprising one or more heteroatoms, at least one among R1, R2 and R3 being chosen in the group of alkenyl, alkynyl, arylalkenyl and arylalkynyl moieties, optionally comprising one or more heteroatoms.