Investigation on synthesis, structure and catalytic modification of Ca(AlH4)2 complex hydride

Ca(AlH4)2 was synthesized by ball-milling the mixture of NaAlH4 and CaCl2 in a molar ratio of 2:1 and under a hydrogen atmosphere of 1 MPa. The dehydrogenation behavior and phase transitions of Ca(AlH4)2 have been investigated during the thermal decomposition process. In addition, doping with TiF3 catalyst was applied to improve the dehydriding kinetics of Ca(AlH4)2. The results show that 10 wt.% TiF3-doped Ca(AlH4)2 exhibits excellent dehydriding performance in the first two-step decomposition reactions, with decomposition temperature dropped by 32 °C and 48 °C respectively, the activation energy for the second step decomposition reaction decreases from 153.4 kJ/mol to 57.4 kJ/mol. Moreover, our study shows that the addition of TiF3 to Ca(AlH4)2 initiated the partially decomposition of Ca(AlH4)2 during the ball-milling treatment, which leads to the release of H2, as well as the generation of Ti element and probably CaAlFxH5−x. These products are ascribed to have catalytic and destabilization effects on the dehydriding kinetics of Ca(AlH4)2 system.