Alanate-borohydride material systems for hydrogen storage applications

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 1st and 2nd 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