Reversible Li-insertion in nanoscaffolds: A promising strategy to alter the hydrogen sorption properties of Li-based complex hydrides

Abstract

Intercalation and de-intercalation of lithium into graphene layers is a well-established phenomenon in Li-ion battery technology. Here we show how this phenomenon can be exploited to destabilize, and alter the hydrogen sorption behaviour of Li-based metal hydrides (LiBH4 and LiAlH4), thereby achieving lower hydrogen release temperatures, high hydrogen sorption capacities and enhanced kinetics. Close contact between the hydride and carbon surface facilitates reversible intercalation of Li into graphene layers at moderate temperatures when nanoconfined in turbostratic carbon nanoscaffolds. This leads to the formation of intercalated Li (LiCx, instead of LiH) during decomposition, resulting in the release of the full hydrogen content at moderate temperatures. For example, LiBH4 nanoconfined in this graphitic carbon material decomposes into LiCx+B and 18.5 wt% H2 (instead of 13.8 wt% H2 for macrocrystalline LiBH4) at temperatures as low as 375 °C under Ar flow. Thermodynamic effects were also observed; the decomposition temperature at 1 bar H2 atmosphere is lowered by ~150 °C compared to the macrocrystalline LiBH4. These finding presents an interesting fundamental insight into interactions between nanoconfined metal hydrides and scaffold materials, and how such interactions can be exploited to generally improve the hydrogen sorption properties of metal hydrides.