Alanate–borohydride material systems for hydrogen storage applications

Alteration of the thermodynamic stability of selected borohydride/alanate systems, including the combination of LiBH4 with NaAlH4 and LiBH4 with CaCl2 and LiAlH4, was investigated to determine the possibility of forming intermediate stability mixed AlH4−–BH4− phase.Facile metathesis exchange reactions were observed when NaAlH4 was combined with LiBH4 resulting in the formation of LiAlH4 and NaBH4. Thermal analysis of this system showed that the 1st and 2nd decomposition of LiAlH4 occurred irrespective of NaBH4 illustrating the absence molecular level interaction between the AlH4− and the BH4− anions. On the other hand, in the case of CaCl2, LiAlH4, LiBH4 combination, the results showed the formation of a calcium alanate type phase. Evaluation of the thermal property of this system showed an endothermic one step decomposition between 130 °C and 200 °C (2.3 wt% loss). Structural examination of this calcium alanate type phase revealed a different local coordination geometry of AlH4− from that observed in calcium alanate. The formation and properties of this phase are being attributed to molecular level AlH4−–BH4− interactions. These findings provide a pathway toward designing novel alanates-borohydrides systems for hydrogen storage applications. This article will show the methodologies followed and explain the results obtained.

► Combination of alanates with borohydrides researched. ► LiBH4-NaAlH4 combination resulted in metathesis reaction. ► The ternary system of LiBH4, CaCl2, LiAlH4 led to a new calcium alanate phase. ► Thermal properties of new phase showed novel stabilization in borohydride presence. ► For the first time, evidence of unique borohydrides interactions with alanates.