Optimizing the Destabilization of LiBH4 for Hydrogen Storage and the Effect of Different Al Sources

Due to its high hydrogen storage capacity of 18.5 wt %, LiBH 4 has gained much attention as a potential onboard hydrogen storage medium for automotive applications. Unfortunately, LiBH 4 only decomposes fully above 600 °C, and hydrogenation does not occur below 600 °C and requires hydrogen pressures of at least 350 bar. However, these conditions can be significantly improved by thermodynamic destabilization. In this study, LiBH 4 was augmented with two different Al-sources (metallic Al and from the decomposition of LiAlH 4 ) and the effectiveness of the different Al sources on the dehydrogenation/hydrogenation behavior was investigated along with the efficacy of using a Ti-based catalyst. Ball milling conditions were also investigated to study the effect of premilling the individual components. It has been found that longer ball-milling times (3 h) for 2LiBH 4:LiAlH 4 in the presence of TiCl 3 resulted in higher H 2 release than reported in the literature. In addition, a lower dehydrogenation temperature and improved reversibility (under 85 bar H 2 and at 350 °C) were achieved for the LiAlH 4 -containing samples than in the case of metallic Al. The TiCl 3 was found to catalyze the decomposition of LiAlH 4 during ball milling, resulting in highly dispersed Al through the LiBH 4 . This proved to be a more effective route to deliver the Al destabilization agent, leading to higher capacities and improved reversibility of the system. Premilling the individual components together prior to the addition of the Ti-catalyst was found to be detrimental to the system, resulting in higher dehydrogenation temperatures than achieved by comilling all the reagents. The enthalpy of dehydrogenation was found to be 38.2 kJ mol –1 (H 2 ) and the temperature for a 1 bar equilibrium pressure was calculated to be in the range 240–300 °C.