Enhancing the dehydrogenation properties of LiAlH4 using K2NiF6 as additive

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 K2NiF6 as an additive to LiAlH4. The addition of K2NiF6 showed an excellent improvement of the LiAlH4 dehydrogenation properties. After adding 10 wt% K2NiF6 , the initial decomposition temperature of LiAlH4 within the first two dehydrogenation steps was lowered to 90 degrees C and 156 degrees C, respectively, that is 50 degrees C and 27 degrees C lower than that of the as-milled LiAlH4. In terms of dehydrogenation kinetics, the dehydrogenation rate of K2NiF6-doped LiAlH4 sample was significantly higher as compared to as-milled LiAlH4. The K2NiF6-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 K2NiF6-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 K2NiF6 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. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, K2NiF6 was used as an additive to improve the dehydrogenation properties of LiAlH4. The addition of K2NiF6 significantly reduced the decomposition temperature and enhanced the dehydrogenation kinetics of LiAlH4. The morphology study showed that the LiAlH4 particles became smaller and less agglomerated when K2NiF6 was added. The in situ formation of new phases during the dehydrogenation process, as well as a reduction in particle size, were believed to contribute to the improved dehydrogenation characteristics of LiAlH4.