Decomposition Reactions and Reversibility of the LiBH₄−Ca(BH₄)₂ Composite

LiBH 4 is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its use in real applications. In an effort to overcome this barrier and to adjust the thermal stability, we make a composite system LiBH 4 −Ca(BH 4 ) 2 . In order to fully characterize this composite system we study x LiBH 4 + (1 − x )Ca(BH 4 ) 2 for several x values between 0 and 1, using differential scanning calorimetry, in situ synchrotron X-ray diffraction, thermogravimetric analysis, and mass spectrometry. Interestingly, this composite undergoes a eutectic melting at ca. 200 °C in a wide composition range, and the eutectic composition lies between x = 0.6 and 0.8. The decomposition characteristics and the hydrogen capacity of this composite vary with x, and the decomposition temperature is lower than both the pure LiBH 4 and Ca(BH 4 ) 2 at intermediate compositions, for example, for x ≈ 0.4, decomposition is finished below 400 °C releasing about 10 wt % of hydrogen. Partial reversibility of this system was also confirmed for the first time for the case of a mixed borohydride composite.