Complex Metal Hydrides for Reversible Hydrogen Storage
Economic and practical hydrogen storage is one of the greatest obstacles to achieving a hydrogen economy. Storage methods such as compressed gas cylinders and cryogenic liquid containers are too inefficient and dangerous for practical use in a hydrogen vehicle. Complex metal hydrides may provide the hydrogen storage solution. Lithium borohydride and aluminum react to form an unknown complex metal hydride. This hydride has the potential to be an efficient and reversible hydrogen storage material. The LiBH4:Al sample releases hydrogen during decomposition at high temperature and can be rehydrogenated (charged) at high pressure and temperature. Titanium catalyzes these reactions. The focus of this research project is the determination of the effects of different charging conditions. The research provides evidence that the addition of aluminum to lithium borohydride creates a complex hydride that decomposes in two steps. Each of these steps is at least partially reversible, allowing for recharging. Higher charging pressures and longer charging times increase the amount of hydrogen that can be stored in the sample. Ball milling the sample prior to charging also increases the hydrogen storage capacity. At the end of this project, the greatest observed reversibility of the sample was 6 wt% for one charge-discharge cycle.