Enhancing the dehydrogenation properties of LiAlH4 using K2NiF6 as additive. (12th July 2022) - Ahmad, M.A.N.
Abstract: Lithium alanate (LiAlH4 ) is a material that can be potentially used for solid-state hydrogen storage due to its high hydrogen content (10.5 wt%). Nevertheless, a high desorption temperature, slow desorption kinetic, and irreversibility have restricted the application of LiAlH4 as a solid-state hydrogen storage material. Hence, to lower the decomposition temperature and to boost the dehydrogenation kinetic, in this study, we applied K2 NiF6 as an additive to LiAlH4 . The addition of K2 NiF6 showed an excellent improvement of the LiAlH4 dehydrogenation properties. After adding 10 wt% K2 NiF6, the initial decomposition temperature of LiAlH4 within the first two dehydrogenation steps was lowered to 90 °C and 156 °C, respectively, that is 50 °C and 27 °C lower than that of the аs-milled LiAlH4 . In terms of dehydrogenation kinetics, the dehydrogenation rate of K2 NiF6 -doped LiAlH4 sample was significantly higher as compared to аs-milled LiAlH4 . The K2 NiF6 -doped LiAlH4 sample can release 3.07 wt% hydrogen within 90 min, while the milled LiAlH4 merely release 0.19 wt% hydrogen during the same period. According to the Arrhenius plot, the apparent activation energies for the desorption process of K2 NiF6 -doped LiAlH4 are 75.0 kJ/mol for the first stage and 88.0 kJ/mol for the second stage. These activation energies are lower compared to the undoped LiAlH4 . The morphology study showed that the LiAlH4 particles become smaller and less agglomerated when K2 NiF6 is added. The in situ formation of new phases of AlNi and LiF during the dehydrogenation process, as well as a reduction in particle size, is believed to be essential contributors in improving the LiAlH4 dehydrogenation characteristics. Highlights: K2 NiF6 showed superior catalytic effects for dehydrogenation properties of LiAlH4 . K2 NiF6 -doped LiAlH4 starts to desorb hydrogen at about 90 °C. K2 NiF6 -doped LiAlH4 could desorb 3.07 wt% H2 within 90 min at 90 °C. The E A for H2 released from LiAlH4 were lowered after the addition of K2 NiF6 . The new phases of AlNi and LiF and reduction in particle sizes play a catalytic role.