Nature Mater. doi:10.1038/nmat2978 (2011)

Hydrogen is a promising alternative energy carrier that can burn without producing carbon dioxide and when used in a fuel cell creates only water as a by-product. Materials are, however, required to store and then release the hydrogen (through a small increase in temperature) when needed. A variety of potential storage materials have been examined, including metal–organic frameworks and carbon-based nanostructures, but in general they are capable of physisorbing only a small quantity of hydrogen at room temperature. Metal hydrides have been of particular interest, but they typically require high temperatures to release the hydrogen. Jeffrey Urban and colleagues at the Lawrence Berkeley National Laboratory and the FEI Company have now shown that magnesium nanocomposites can store a high density of hydrogen with rapid storage kinetics.

The nanocomposites are synthesized using a one-pot, room-temperature reaction in which an organometallic Mg2+ precursor is reduced in the presence of a soluble organic polymer called PMMA. The reaction creates metallic magnesium nanocrystals encapsulated by the polymer. The polymer provides a gas-selective barrier to the magnesium nanocrystals that allows the nanocrystals to absorb and release hydrogen while protecting them from oxygen and water, which are detrimental to their hydrogen storage capabilities.

Urban and colleagues find that the nanocomposites exhibit rapid hydrogen uptake with a storage capacity of up to 6 wt% of magnesium and a volumetric capacity greater than that of compressed hydrogen gas.