A NaAlH4-Ca(BH4)2 composite system for hydrogen storage

- Ca(AlH4)2 is formed in a metathesis reaction between NaAlH4 and Ca(BH4)2.
- Increasing the ball-milling time increases the yield of Ca(AlH4)2.
- Thermal treatment enhances the metathesis reaction too.
- Ca(AlH4)2 decomposes in two steps below 200 °C releasing ∼2.8 wt% H2.

Mechanochemical treatment (ball-milling) of NaAlH4-Ca(BH4)2 mixtures leads to partial formation of NaBH4 and Ca(AlH4)2 by a metathesis reaction. The reaction proceeds to different extents depending on the applied ball-milling times, which is confirmed by powder X-ray diffraction and infrared spectroscopy. Additionally, an in-situ synchrotron radiation powder X-ray diffraction study reveals that the metathesis reaction continues due to thermal treatment while the data also supports a two-step decomposition of the formed Ca(AlH4)2. Finally, the reactive hydride composite system was investigated by mass spectrometry and Sieverts' measurement, which reveal release of ∼6 wt% H2 at T < 400 °C.

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