Hydrogen Storage: Size Effects in Complex Hydrides

Hydrogen is recognised as a promising alternative to fossil fuel based energy carriers. However storing hydrogen remains the ultimate barrier to its implementation. Complex hydride materials are potential hydrogen stores but their properties require some modifications to meet the targets set for market implementation, i.e. 6 wt % hydrogen capacity and reversible storage under moderate temperatures and pressures [1]. To date, several approaches have been considered unsuccessfully, including nanostructuring [2], destabilisation with other hydrides to improve thermodynamics [3], and the use of catalysts to enhance kinetics [4]. Theoretical modelling has guided experimental work but synthesising the resulting compounds remains challenging [5]. As the properties of nanomaterials are size dependent [5], herein we have used carbon nanotubes to encapsulate hydride nanoparticles, facilitating investigations with respect to size effects. Preliminary results demonstrate that the thermodynamic and desorption kinetics of complex hydrides confined to the nanometre range are significantly improved: e.g. hydrogen desorption occurred below 100°C instead of 600°C for LiBH4. Further research is underway to develop the strategy. The future implications of this observation will be discussed.