Effects of NbF5 addition on the hydrogen storage properties of LiAlH4

We investigated the effects of NbF5 addition by ball milling on the hydrogen storage properties of LiAlH4. Pressure-composition-temperature (PCT) experiments showed that addition of 0.5 and 1 mol% NbF5 in LiAlH4 improves the onset desorption temperature and results in little decrease in hydrogen capacity, with approximately 7.0 wt% released by 188 degrees C. Isothermal dehydriding kinetics measurements indicated that the NbF5-doped sample shows an average dehydrogenation rate 5-6 times faster than that of the as-received LiAlH4 sample. In the x-ray diffraction results, there are distinct peaks of Al and LiH that appear after desorption. There is no peak of NbF5 before or after desorption. Desorption kinetics measurements indicated that the activation energy, E-A, for LiAlH4 + 1 mol% NbF5 is about 67 kJ/mol for first reaction stage and about 77 kJ/mol for second reaction stage. The desorption process was further characterised by differential scanning calorimetry, and the possible mechanism of the effects of NbF5 addition is discussed. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.