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

Abstract

LiBH4 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 LiBH4-Ca(BH4)(2). In order to fully characterize this composite system we study xLiBH(4) + (1 - x)Ca(BH4)(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 degrees 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 LiBH4 and Ca(BH4)(2) at intermediate conpositions, for example, for x approximate to 0.4, decomposition is finished below 400 degrees C releasing about 10 wt % of hydrogen. Partial reversibility of this system was also confirmed for the first time for the case of if mixed borohydride composite.