Reversibility of LiBH₄ Facilitated by the LiBH₄–Ca(BH₄)₂ Eutectic

Abstract

The hydrogen storage properties of eutectic melting 0.68LiBH4–0.32Ca­(BH4)2 (LiCa) as bulk and nanoconfined into a high surface area, S BET = 2421 ± 189 m2/g, carbon aerogel scaffold, with an average pore size of 13 nm and pore volume of V tot = 2.46 ± 0.46 mL/g, is investigated. Hydrogen desorption and absorption data were collected in the temperature range of RT to 500 °C (ΔT/Δt = 5 °C/min) with the temperature then kept constant at 500 °C for 10 h at hydrogen pressures in the range of 1–8 and 134–144 bar, respectively. The difference in the maximum H2 release rate temperature, T max, between bulk and nanoconfined LiCa during the second cycle is ΔT max ≈ 40 °C, which over five cycles becomes smaller, ΔT max ≈ 10 °C. The high temperature, T max ≈ 455 °C, explains the need for high temperatures for rehydrogenation in order to obtain sufficiently fast reaction kinetics. This work also reveals that nanoconfinement has little effect on the later cycles and that nanoconfinement of pure LiBH4 has a strong effect in only the first cycle of H2 release. The hydrogen storage capacity is stable for bulk and nanoconfined LiCa in the second to the fifth cycle, which contrasts to nanoconfined LiBH4 where the H2 storage capacity continuously decreases. Bulk and nanoconfined LiCa have hydrogen storage capacities of 5.4 and 3.7 wt % H2 in the fifth H2 release, which compare well with the calculated hydrogen contents of LiBH4 only and in LiCa, which are 5.43 and 3.69 wt % H2, respectively. Thus, decomposition products of Ca­(BH4)2 appear to facilitate the full reversibility of the LiBH4, and this approach may lead to new hydrogen storage systems with stable energy storage capacity over multiple cycles of hydrogen release and uptake.

Reactive Hydride Composite of Mg2NiH4 with Borohydrides Eutectic Mixtures

“…In the 2nd cycle (Figure 6b, 2nd cycle), all the previous transitions of the LiCa system are observed. At higher temperatures, the polymorphic transition of Mg 2 NiH 4 is detected at T peak = 243 • C, together with a small peak of hydrogen release from the liquid borohydride, as previously observed in the MgNiLiMg system and in the literature [37]. Furthermore, a DSC endothermic peak due to hydrogen release starts above 300 • C (T peak = 332 • C), under 2.7 bar H 2 , so that heating has been stopped at 350 • C, in order to separate hydrogen release reactions.…”

A Review of the MSCA ITN ECOSTORE—Novel Complex Metal Hydrides for Efficient and Compact Storage of Renewable Energy as Hydrogen and Electricity

“…An even lower desorption temperature has been registered for high surface area CO 2 activated aerogel carbon, with a difference between bulk and infiltrated material of 95 • C and the main desorption peak occurring at 298 • C compared to 393 • C for the bulk [246]. However, the improvements registered for the first desorption are gradually lost within five hydrogenation cycles [387].…”

A Review of Thermochemical Energy Storage Systems for Power Grid Support

“…Also the interest towards metal hydrides is not recent, these thermochemical storage systems were explored since the mid-1970s [264]. Several applications and different metal hydrides systems were explored for thermochemical heat storage [265][266][267][268][269]. Among metal hydrides, Mg-based systems are promising as thermochemical storage materials owing to high reaction enthalpy as shown in the studies of Gigantino et al [223] and Shkatulov et al [53].…”

“…Kuwata et al [302] investigated the potential of the ammonium chloride SrCl 2 in applications based on utilization of industrial waste heat. Thermochemical energy storage could be a key technology able to bridge the gap between the wasted heat as the source and provided to customers at the time and place they need it [267,268]. A more detailed review on this field was developed in [304].…”