Improvement of the LiAlH₄−NaBH₄ System for Reversible Hydrogen Storage

Abstract

The hydrogen storage properties of a combined LiAlH4−NaBH4 system have been investigated. It was found that there is a mutual destabilization between the LiAlH4 and the NaBH4. Two major dehydrogenation steps with hydrogen capacities of 3.1 wt % and 5.2 wt % were observed for the system with a molar ratio of LiAlH4:NaBH4 = 1:1 at around 250 and 600 °C, respectively. The onset dehydrogenation temperatures for the first and the second steps in the LiAlH4−NaBH4 mixture were decreased to 95 and 450 °C, respectively, which are 30 and 50 °C lower than those of bare LiAlH4 and NaBH4, respectively. Furthermore, doping with TiF3 significantly decreases the hydrogen release temperature compared to the undoped system. The TiF3 doping can further decrease the onset temperatures of the first and second steps to 60 and 300 °C. The presence of TiF3 also destabilizes the NaH phase, which leads to an increased desorption capacity. Pressure−composition−temperature (PCT) and van’t Hoff plots illustrate that the decomposition enthalpy of NaBH4 in the TiF3-doped LiAlH4−NaBH4 system is decreased from 106.8 kJ/(mol of H2) for pure NaBH4 to 68.16 kJ/(mol of H2). In addition, about 4 wt % hydrogen can be reversibly stored by the dehydrogenated product, and the formation of NaBH4 was detected by X-ray diffraction in the rehydrogenated sample.

Hydrogen storage properties and mechanisms of the Mg(BH4)2–NaAlH4 system

“…Specifically, the reversible hydrogen storage capacity is lower than the dehydrogenation amount of the as-milled sample, implying a partial reversibility. However, only w2.3 wt% of hydrogen is charged into the dehydrogenated Mg(AlH 4 ) 2 under the same conditions, and even no hydrogen absorption is detected for the dehydrogenated NaBH 4 [40,41]. It can be therefore concluded that combining NaBH 4 and Mg(AlH 4 ) 2 significantly improves hydrogen storage reversibility.…”

A Revisit to the Hydrogen Desorption/Absorption Behaviors of LiAlH4/LiBH4: Effects of Catalysts

“…After the hydrogen desorption at 300 °C ( Figure 5), Al and LiH are present in both undoped and doped mixtures, without the formation of AlB 2 . It is the AlB 2 phase that is claimed to facilitate the reversibility of LiAlH 4 and LiBH 4 [11,[14][15][16]]. This could be a possible reason why the LiAlH 4 /LiBH 4 mixture is not reversible.…”

Recent Advances in the Use of Sodium Borohydride as a Solid State Hydrogen Store

“…By employing this strategy, the dehydrogenation of NaBH4 can be facilitated by combining the borohydride with other metal hydrides such as LiAlH4, Ca(BH4)2 and CaH2 so as to form LiAl, AlB2 and CaB6 respectively upon dehydrogenation [27,44]: 2NaBH4 + 2LiAlH4 → 2Na + AlB2 + LiAl + 8H2 10.6 wt% (5) 4NaBH4 + Ca(BH4)2 → 4Na + CaB6 + 12H2 10.9 wt% (6) 6NaBH4 + CaH2 → 6Na + CaB6 + 13H2 9.7 wt% (…”