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The catalytic effect of K 2 SiF 6 on MgH 2 was first timely studied. The MgH 2 + 5 wt.% K 2 SiF 6 was prepared via the ball milling technique. The catalyst had lessened the initial decomposition temperature by 134 °C and 48 °C as compared to both pristine and milled MgH 2 samples, respectively. In 2 minutes, 4.5 wt.% of hydrogen was absorbed (250 °C) by the doped composite, which was 0.8 wt.% higher than the milled MgH 2. Meanwhile, for the desorption kinetics (320 °C, 1 atm), the amount of desorbed hydrogen was increased by 2.4 wt.% and 2.3 wt.% for the first 10 and 20 minutes. Besides, contracting volume and Johnson-Mehl-Avrami models were used to analyse the kinetics sorptions. The decomposition activation energy calculated based on Kissinger equation was 114 kJ/mol. As for the active species, Mg 2 Si, MgF 2 and KH were formed during the heating process. These active species are speculated to be responsible for the improvement of the hydrogenation properties of the composite. [ABSTRACT FROM AUTHOR]

Abstract Investigations on the catalytic effects of a non-reactive and stable additive, SrTiO 3 , on the hydrogen storage properties of the 4MgH 2 Na 3 AlH 6 destabilized system were carried out for the first time. The Na 3 AlH 6 compound and the destabilized systems used in the investigations are prepared using ball milling method. The doped system, 4MgH 2 Na 3 AlH 6 SrTiO 3 , had an initial dehydrogenation temperature of 145 °C, which 25 °C lower as compared to the un-doped system. The isothermal absorption and desorption capacity at 320 °C has increased by 1.2 wt% and 1.6 wt% with the addition of SrTiO 3 as compared to the 4MgH 2 Na 3 AlH 6 destabilized system. The decomposition activation energy of the doped system is estimated to be 117.1 kJ/mol. As for the XRD analyses at different decomposition stages, SrTiO 3 is found to be stable and inert. In addition to SrTiO 3 , similar phases are found in the doped and the un-doped system during the decomposition and dehydrogenation processes. Therefore, the catalytic effect of the SrTiO 3 is speculated owing to its ability to modify the physical structure of the 4MgH 2 Na 3 AlH 6 particles through pulverization effect. Highlights • H 2 storage properties of SrTiO 3 -doped 4MgH 2 Na 3 AlH 6 composite were investigated. • Doped with SrTiO 3 improved the H 2 sorption properties of 4MgH 2 Na 3 AlH 6. • The activation energy of the doped system is reduced to 117.1 kJ/mol. • SrTiO 3 give a pulverization effect for the SrTiO 3 -doped 4MgH 2 Na 3 AlH 6 composite. [ABSTRACT FROM AUTHOR]

The catalytic effects of K 2 NbF 7 on the hydrogen storage properties of MgH 2 have been studied for the first time. MgH 2 + 5 wt% K 2 NbF 7 has reduced the onset dehydrogenation temperature to 255 °C, which is 75 °C lower than the as-milled MgH 2 . For the rehydrogenation kinetic, at 150 °C, MgH 2 + 5 wt% K 2 NbF 7 absorbs 4.7 wt% of hydrogen in 30 min whereas the as-milled MgH 2 only absorbs 0.7 wt% of hydrogen under similar condition. For the dehydrogenation kinetic, at 320 °C, the MgH 2 + 5 wt% K 2 NbF 7 is able to release 5.2 wt% of hydrogen in 5.6 min as compared to 0.3 wt% by the as-milled MgH 2 under similar condition. Comparatively, the E a value of MgH 2 + 5 wt% K 2 NbF 7 is 96.3 kJ/mol, which is 39 kJ/mol lower compared to the as-milled MgH 2 . The MgF 2 , the KH and the Nb that are found after the heating process are believed to be the active species that have improved the system properties. It is concluded that the K 2 NbF 7 is a good catalyst to improve the hydrogen storage properties of MgH 2 . [ABSTRACT FROM AUTHOR]

In this work, we investigated the effects of BaFe 12 O 19 on the dehydrogenation properties of LiAlH 4. It was shown that the LiAlH 4 doped with 10 wt% of BaFe 12 O 19 had started to release hydrogen at 95 °C, as compared with undoped LiAlH 4 (more than 140 °C). Desorption kinetic result showed that the BaFe 12 O 19 -doped LiAlH 4 sample can release more hydrogen (4.2 wt% of H 2) compared to undoped LiAlH 4 (less than 1.0 wt%) at 90 °C for 2.5 h. Results of differential scanning calorimetry measurements showed that the thermal events had remained the same for the BaFe 12 O 19 –doped LiAlH 4 sample and the undoped LiAlH 4. However, thermal events occurred at a lower temperature after the addition of 10 wt% BaFe 12 O 19. The desorption activation energies of the first two reactions for the BaFe 12 O 19 –doped LiAlH 4 sample were decreased by about 32 kJ/mol and 22 kJ/mol, compared to undoped LiAlH 4 , respectively. Scanning electron microscopy images revealed the size of particles became smaller with the addition of BaFe 12 O 19. It is believed that the improvements in the desorption process were catalysed by the Fe, LiFeO 2 and amorphous Ba or Ba-containing that were formed in situ during the dehydrogenation process. • BaFe 12 O 19 showed superior catalytic effects for LiAlH 4. • BaFe 12 O 19 -doped LiAlH 4 could desorb 4.2 wt% H 2 within 2.5 h at 90 °C. • The new species of Fe, LiFeO 2 and Ba-containing play a synergistic catalytic role. [ABSTRACT FROM AUTHOR]

The influences of MgNiO 2 nanoflakes that are synthesised via a simple hydrothermal method on the hydrogen sorption performance of MgH 2 are studied for the first time. The temperature-programmed desorption curve shows that when 10 wt% of MgNiO 2 is added to MgH 2 , hydrogen has started to release at 258 °C in comparison to the milled MgH 2 , which has released at 340 °C. The absorption kinetics for the MgNiO 2 -doped MgH 2 sample demonstrates great hydrogen absorption with the capacity of hydrogen is up to 6.1 wt% within 10 min at 200 °C, while the milled MgH 2 has only absorbed about 4.4 wt%. In terms of desorption kinetics, the MgNiO 2 -doped MgH 2 sample has shown faster desorption with 5.1 wt% of hydrogen is released in a duration of 10 min while the milled MgH 2 has only released about 0.6 wt% of hydrogen. The Arrhenius plot shows that doping MgH 2 with MgNiO 2 has lowered the activation energy to 108.0 kJ mol−1, a decrease of 52.0 kJ mol−1 in comparison to the as-milled MgH 2 (160.0 kJ mol−1). It is believed that the formations of new compounds, MgO and NiO, act as active species and offer significant synergetic catalytic effect, thus improving the hydrogen storage performance of MgH 2. • MgNiO 2 nanoflakes are prepared via a simple hydrothermal method. • MgNiO 2 nanoflakes showed superior catalytic effects for MgH 2. • MgNiO 2 -doped MgH 2 could desorb 5.1 wt% H 2 within 10 min at 320 °C. • MgNiO 2 -doped MgH 2 could absorb 6.1 wt% H 2 within 10 min at 200 °C. • The new species of MgO and NiO play a synergistic catalytic role. [ABSTRACT FROM AUTHOR]