The present invention provides for a composition capable of storing hydrogen from molecular hydrogen. The composition comprises a magnesium nanoparticle (NP) and a polymer, wherein the Mg NC is essentially embedded in the polymer. The polymer is selectively permeable wherein the polymer is essentially not permeable to O.sub.2 and H.sub.2O. The composition is capable of absorbing and desorbing molecular hydrogen.
STATEMENT OF GOVERNMENTAL SUPPORT
 This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in the invention.