Intensive investigation on hydrogen storage properties and reaction mechanism of the NaBH4-Li3AlH6 destabilized system

Abstract Notable effects of Li 3 AlH 6 on the hydrogen storage properties of the NaBH 4 are studied intensively. Li 3 AlH 6 is synthesized by milling 2LiH-LiAlH 4 mixture for 12 h. The best molar ratio of the NaBH 4 - Li 3 AlH 6 destabilized system is 1:1 which has decomposed at two stages; Li 3 AlH 6 decomposition stage at 170 °C and NaBH 4 decomposition stage at 400 °C. As no significant effect on the decomposition temperature between 1 h and 24 h of milling time can be observed, the 1-hour milling preparation method is selected for the characterization. Isothermal absorption has shown that the system is able to absorb 4.2 wt% and 6.1 wt% of hydrogen in 60 min at 330 °C and 420 °C under 30 atm of hydrogen pressure. In contrast, only about 3.4 wt% and 3.7 wt% of hydrogen can be absorbed by the milled NaBH 4 under a similar condition. Meanwhile, the system is able to desorb 2.0 wt% and 4.1 wt% of hydrogen in 60 min at 330 °C and 420 °C in isothermal desorption while only 0.3 wt% and 2.1 wt% can be released by the milled NaBH 4 under the similar condition. The decomposition activation energy and enthalpy of the NaBH 4 stage are calculated to be 162.1 kJ/mol and 68.1 kJ/mol H 2 . Based on the X-ray diffraction analysis, Na, Al and AlB 2 are formed during the dehydrogenation process. The formation of Al and AlB2 are the keys to the improvement of hydrogenation properties. It is concluded that Li 3 AlH 6 is a good destabilizing agent for the NaBH 4 system.