Alanate-borohydride material systems for hydrogen storage applications

摘要

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-BHi 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 A1H_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 ℃ and 200 ℃ (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.