Today's technology is capable of powering a car using hydrogen reducing harmful emissions to zero. Yet there is no safe, low-cost way to store hydrogen. Scientists at the ISIS neutron source are developing new materials that could put hydrogen power onto our roads and into our homes.
Carbon-based nano-structured materials are lightweight and have large surface areas, but molecular hydrogen (H2) is known to have a feeble interaction in graphite-like materials making them unsuitable for room temperature use.
But injecting alkali metals into graphite increases the quantity of hydrogen that can be stored. These ‘graphite intercalation compounds’ are easily made, and each layer of guest atoms is separated by a regular number of graphite layers.
New insights into hydrogen binding sites in the blue-coloured potassium graphite intercalate KC24 have been gained using a combination of neutron spectroscopy and computer modelling [Lovell et al., Phys. Rev. Lett. (2008) 101 126101].
The results show that quantum effects can reduce the quantity of stored hydrogen in this type of material by over 60 percent. Three sites for trapping hydrogen are available around each alkali atom, but delocalisation of the hydrogen molecule across the sites prevents additional molecules settling in.