Abstract
Hydrogen is a potential green alternative to conventional energy carriers such as oil and coal. Compared with the storage of hydrogen in gaseous or liquid phases, the chemical storage of hydrogen in solid complex hydrides is safer and more effective. In this study, the complex hydride composite 2LiBH4–Li3AlH6 with different amounts of TiF3 was prepared by simple ball-milling and its hydrogen storage properties were investigated. Temperature programmed desorption and differential scanning calorimetry were used to characterize the de/rehydrogenation performance, and X-ray diffraction and scanning electron microscopy (SEM) were used to explore the phase structure and surface topography of the materials. The dehydrogenation temperature decreased by 48°C in 2LiBH4–Li3AlH6 with 15 wt% TiF3 composites compared to the composite without additives while the reaction kinetics was accelerated by 20%. In addition, the influence of hydrogen back pressure on the 2LiBH4–Li3AlH6 with 5 wt% TiF3 composite was also investigated. The results show that hydrogen back pressure between 2.5 and 3.5 bar can improve the reversible performance of the composite to some extent. With a back pressure of 3.5 bar, the second dehydrogenation capacity increased to 4.6 wt% from the 3.3 wt% in the 2LiBH4–Li3AlH6 composite without hydrogen back pressure. However, the dehydrogenation kinetics was hindered. About 150 h, which is 100 times the time required without back pressure, was needed to release 8.7 wt% of hydrogen at 3.5 bar hydrogen back pressure. The SEM results show that aluminum was aggregated after the second cycle of dehydrogenation at the hydrogen back pressure of 3 bar, resulting in the partial reversibility of the 5 wt% TiF3-added 2LiBH4–Li3AlH6 composite.
Highlights
As a new energy source, hydrogen has great potential to solve the serious energy depletion and atmospheric pollution caused by excessive utilization of conventional energy sources
A possible reason for this is the partial decomposition of Li3AlH6 during the ball-milling process (Liu, 2010). This result is consistent with the XRD patterns (Figure 2), in which LiH and Al were detected in the TiF3-added ball-milling samples, and indicates that TiF3 is an effective catalyst that can destabilize Li3AlH6 at a lower temperature
Faster dehydrogenation kinetics were obtained as the dehydrogenation peak of LiBH4 became broader with the increase in the amount of TiF3 (Zang, et al, 2018)
Summary
As a new energy source, hydrogen has great potential to solve the serious energy depletion and atmospheric pollution caused by excessive utilization of conventional energy sources. The calorific value of 1 kg of hydrogen is 140 megajoules of energy, which is three times of that of the amount of energy released by the same weight of oil. Water vapor is the only combustion product of hydrogen, making it a pollution-free energy source. The limitations of hydrogen storage technology have hindered its practical application. As a promising candidate for solid-state hydrogen storage, LiBH4 has a high theoretical gravimetric hydrogen density of 18.5 wt%, which is the highest among all the solid hydride materials. The material released 0.3 wt% hydrogen at 200°C and 1 wt % hydrogen at 320°C. After heating to 500°C, rapid hydrogen desorption was observed, and 9 wt% of hydrogen was released
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