The effects of nanoconfinement on the structural phase transition, H 2 release and uptake, and the emission of toxic diborane (B 2 H 6 ) on desorption of LiBH 4 have been comprehensively investigated in the presence of various porous hard carbon templates at a variety of pore sizes. Calorimetry signatures of both the structural phase transition and melting of nanoconfined LiBH 4 shifted to a lower temperature with respect to the bulk, finally vanishing below a pore size around 4 nm. The desorption of LiBH 4 confined in these nanoporous carbons shows a systematic and monotonic decrease in the desorption temperature and concomitantly, mass spectroscopic analysis indicated a gradual reduction of the partial pressure of B 2 H 6 with decreasing pore size, suggesting that formation of stable closoborane salts may be avoided by interrupting the reaction pathway. This represents a major breakthrough in the reversibility of boron-based hydrogen storage systems, where capacity is lost in the formation of stable B-H species on cycling. Different carbon preparation techniques suggest that the confinement size, and not solely surface interactions, may be used to tune the properties of complex hydrides for kinetic and reaction pathway improvements for hydrogen storage applications.

The wetting and decomposition behavior of LiBH 4 has been investigated in the presence of highly ordered nanoporous hard carbon (NPC) with hexagonally packed 2 nm diameter columnar pores. Calorimetry, X-ray diffraction, and IR spectroscopy measurements confirm that the LiBH 4 within the pores is amorphous. The confinement of LiBH 4 in such small pores results in the disappearance of the low-temperature structural phase transition, the melting transition, and also the significant decrease of the onset desorption temperature from 460 to 220 °C with respect to bulk LiBH 4 , a lower temperature than observed in larger pore sizes in the literature. Most importantly, our results suggest that diborane release is suppressed or eliminated in the decomposition of noncrystalline LiBH 4 . Tight nanoconfinement may therefore mitigate both safety concerns and loss of active material in borohydride-based hydrogen storage systems.