Tailoring the hydrogen storage properties of Li4BN3H10 by confinement into highly ordered nanoporous carbon

Abstract

The effects of nanoconfinement on the H2 release and uptake, and the emission of toxic ammonia (NH3) and diborane (B2H6) during the decomposition of quaternary phase Li4BN3H10 have been comprehensively investigated. Li4BN3H10 confined in highly ordered nanoporous carbon (Li4BN3H10@NPC) with cylindrical pores and an average pore size of 4.4 nm (NPC-4.4 nm) did not show Bragg peaks or melting of the Li4BN3H10 due to nanoconfinement-induced amorphization. Li4BN3H10 confined in NPC starts to decompose at 110 °C, lower by more than 160 °C with respect to bulk and the dehydrogenation kinetics was significantly enhanced. More importantly, in comparison with the exothermic decomposition of bulk Li4BN3H10, a distinct two-step endothermic decomposition process was observed in the nanoconfined Li4BN3H10 system indicating the decomposition pathway was altered by nanoconfinement. A direct line-of-site residual gas analyzer mass-spectrometer (RGA-MS) analysis indicated NH3 was released earlier than H2 during the decomposition of nanoconfined Li4BN3H10 but it evolved slowly and the overall emissions of NH3 and B2H6 were significantly suppressed by nanoconfinement. More interestingly, some other possible gases, diimine (N2H2) and triborane or heavier species, produced during the decomposition of Li4BN3H10 or its constituent parts (LiBH4 and LiNH2), were identified by RGA-MS for the first time. The observation of diimine in the reaction product may provide insight into the reaction mechanisms for rehydriding of compounds in the LiNH2 and Li2NH systems as well.