Alanate–borohydride material systems for hydrogen storage applications

Abstract

Alteration of the thermodynamic stability of selected borohydride/alanate systems, including the combination of LiBH 4 with NaAlH 4 and LiBH 4 with CaCl 2 and LiAlH 4, was investigated to determine the possibility of forming intermediate stability mixed AlH 4 −–BH 4 − phase. Facile metathesis exchange reactions were observed when NaAlH 4 was combined with LiBH 4 resulting in the formation of LiAlH 4 and NaBH 4. Thermal analysis of this system showed that the 1 st and 2 nd decomposition of LiAlH 4 occurred irrespective of NaBH 4 illustrating the absence molecular level interaction between the AlH 4 − and the BH 4 − anions. On the other hand, in the case of CaCl 2, LiAlH 4, LiBH 4 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 AlH 4 − from that observed in calcium alanate. The formation and properties of this phase are being attributed to molecular level AlH 4 −–BH 4 − 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.