Effect of K2NbF7 on the hydrogen release behaviour of NaAlH4

We explored the influences of the addition of K2NbF7 by mechanical-milling on the dehydrogenation properties of NaAlH4. The results revealed that the addition of K2NbF7 to NaAlH4 decreases the dehydrogenation temperature and improves the dehydrogenation kinetic. The 10 wt% K2NbF7-doped NaAlH4 starts to desorb hydrogen at ∼100 °C and ∼204 °C for the first and second stages of dehydrogenation, respectively, which were ∼80 °C and ∼36 °C lower than the as-milled NaAlH4. For the dehydrogenation kinetic measurement at 150 °C, the K2NbF7-doped NaAlH4 releases ∼2.0 wt% hydrogen in 25 min, which is 10 times faster than as-milled NaAlH4. From the Kissinger calculation, the activation energies for the dehydrogenation process of K2NbF7-doped NaAlH4 are ∼84.6 kJ mol−1 for the first stage of dehydrogenation and ∼75.1 kJ mol−1 for the second stage of dehydrogenation. These activation energies are lower, about 33.3 and 44.9 kJ mol−1, compared with the undoped NaAlH4. The catalytic role of the active species (NbF4 and Al3Nb) that formed during the heating process and the reduction of particle size due to the milling process are the factors that presumably influence the reduction of the onset decomposition temperature and improvement in the dehydrogenation kinetic of the K2NbF7-doped NaAlH4 composite. •K2NbF7 showed superior catalytic effects for dehydrogenation behaviors of NaAlH4.•K2NbF7-doped NaAlH4 starts to desorb hydrogen at ∼100 °C.•K2NbF7-doped NaAlH4 could desorb 2.0 wt% H2 within 25 min at 150 °C.•The new species of NbF4 and Al3Nb play catalytic role.