2LiBH4–MgH2–0.13TiCl4 confined in nanoporous structure of carbon aerogel scaffold for reversible hydrogen storage

Abstract

The investigations based on kinetic improvement and reaction mechanisms during melt infiltration, dehydrogenation, and rehydrogenation of nanoconfined 2LiBH4–MgH2–0.13TiCl4 in carbon aerogel scaffold (CAS) are proposed. It is found that TiCl4 and LiBH4 are successfully nanoconfined in CAS, while MgH2 proceeds partially. In the same temperature (25–500°C) and time (0–5h at constant temperature) ranges nanoconfined 2LiBH4–MgH2–0.13TiCl4 dehydrogenates completely 99% of theoretical H2 storage capacity, while that of nanoconfined 2LiBH4–MgH2 is only 94%. Nanoconfined 2LiBH4–MgH2–0.13TiCl4 performs three-step dehydrogenation at 140, 240, and 380°C. Onset (the first-step) dehydrogenation temperature (140°C), significantly lower than those of nanoconfined sample of 2LiBH4–MgH2 and 2LiBH4–MgH2–TiCl3 (ΔT=140 and 110°C, respectively) is in agreement with the decomposition of eutectic LiBH4–Mg(BH4)2 and lithium–titanium borohydride. For the second and third steps (240 and 380°C), decompositions of LiBH4 destabilized by LiCl solvation and MgH2 are accomplished, respectively. In conclusion, dehydrogenation products are B, Mg, LiH, and TiH. Reversibility of nanoconfined 2LiBH4–MgH2–0.13TiCl4 sample is confirmed by the recovery of LiBH4 after rehydrogenation together with the formation of [B12H12]− derivatives. The superior kinetics during the 2nd, 3rd, and 4th cycles of nanoconfined 2LiBH4–MgH2–0.13TiCl4 to the nanoconfined 2LiBH4–MgH2 can be due to the formations of Ti–MgH2 alloys (Mg0.25Ti0.75H2 and Mg6TiH2) during the 1st rehydrogenation.