Abstract
We investigated the effects of NbF 5 addition by ball milling on the hydrogen storage properties of LiAlH 4. Pressure-composition-temperature (PCT) experiments showed that addition of 0.5 and 1 mol% NbF 5 in LiAlH 4 improves the onset desorption temperature and results in little decrease in hydrogen capacity, with approximately 7.0 wt% released by 188 °C. Isothermal dehydriding kinetics measurements indicated that the NbF 5-doped sample shows an average dehydrogenation rate 5–6 times faster than that of the as-received LiAlH 4 sample. In the x-ray diffraction results, there are distinct peaks of Al and LiH that appear after desorption. There is no peak of NbF 5 before or after desorption. Desorption kinetics measurements indicated that the activation energy, E A, for LiAlH 4 + 1 mol% NbF 5 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 NbF 5 addition is discussed.
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