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Int. J. Electroactive Mater. 6 (2018) 48-56

Improved the Dehydrogenation Properties of Na3AlH6 by Milling With NbF5 Additive

Firdaus Asyraf Halim Yap1, Ahmad Azmin Mohammad2, MOHAMMAD ISMAIL3*

1School of Ocean Engineering, Universiti Malaysia Terengganu, Kuala Nerus, Terengganu, Malaysia
2School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Nibong Tebal, Pulau Pinang, Malaysia
3Department of Physical Sciences, Universiti Malaysia Terengganu, Kuala Terengganu, Terengganu, Malaysia

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Abstract : In this article, the dehydrogenation properties of Na3AlH6 doped with X wt% of NbF5 (X=5, 10, 15, 20) was studied for the first time. The Na3AlH6 composite has formed after 20 h of mechanical alloying between NaH and NaAlH4 (in a mole ratio of 2:1) as observed by X-ray diffraction measurement. Temperature-programmed-desorption results displayed that the decomposition temperature of milled Na3AlH6 was reduced after adding with NbF5 along with the improvement of desorption kinetics behaviors. The onset desorption temperature of Na3AlH6 doped with NbF5 starts at around 180-195 °C, while the decomposition process of Na3AlH6 alone starts at a temperature of 225 °C. Results obtained shows that the 10 wt% of NbF5 additives promote better effect on the dehydrogenation properties of the Na3AlH6 as compared with other samples. From the Kissinger analysis, the apparent activation energy of Na3AlH6 added with 10 wt% NbF5 composite was reduced about 31 kJ/mol as compared to Na3AlH6 alone. The observation of SEM image have shown that the composite particles is less agglomerate. Based on the X-ray diffraction measurement, the new phase of NaF and Al-Nb in the doped composite were observed after the decomposition process. These two species were believed to provide a synergistic effect in accelerating the dehydrogenation properties of the Na3AlH6.

Keywords : hydrogen storage,complex hydrides,dehydrogenation properties,catalys