Search

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]

The addition of a catalyst and ball milling process was found to be one of the efficient method to reduce the decomposition temperature and improve the desorption kinetics of lithium aluminium hydride (LiAlH 4). In this paper, a transition metal oxide, LaFeO 3 was used as a catalyst. Decomposition temperature of the 10 wt% of LaFeO 3 -doped LiAlH 4 system was found to be lowered from 143 °C to 103 °C (first step) and from 175 °C to 153 °C (second step), respectively. In isothermal desorption kinetics, the amount of hydrogen released of the doped sample was improved to 3.9 wt% in 2.5 h at 90 °C. Meanwhile, the undoped sample had released less than 1.0 wt% of hydrogen under the same condition. The activation energy of the LaFeO 3 -doped LiAlH 4 sample was measured to be 73 kJ/mol and 90 kJ/mol for the first two dehydrogenation reactions compared to 107 kJ/mol and 119 kJ/mol for the undoped sample. The improvements of desorption properties were the results from the formation of LiFeO 2 , Fe and La or La-containing phase during the heating process. • The H 2 storage properties of LiAlH 4 /LaFeO 3 have been studied for the first time. • Dehydrogenation properties of LiAlH 4 are improved after adding with LaFeO 3. • The LiAlH 4 /LaFeO 3 composite releases 3.9 wt% in 2.5 h at 90 °C. • The formation of LiFeO 2 , Fe and La or La-containing phase plays a catalytic role. [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]

Currently, magnesium hydride (MgH 2) as a solid-state hydrogen storage material has become the subject of major research owing to its good reversibility, large hydrogen storage capacity (7.6 wt%) and affordability. However, MgH 2 has a high decomposition temperature (>400 °C) and slow desorption and absorption kinetics. In this work, BaMnO 3 was synthesized using the solid-state method and was used as an additive to overcome the drawbacks of MgH 2. Interestingly, after adding 10 wt% of BaMnO 3 , the initial desorption temperature of MgH 2 decreased to 282 °C, which was 138 °C lower than that of pure MgH 2 and 61 °C lower than that of milled MgH 2. For absorption kinetics, at 250 °C in 2 min, 10 wt% of BaMnO 3 -doped MgH 2 absorbed 5.22 wt% of H 2 compared to milled MgH 2 (3.48 wt%). Conversely, the desorption kinetics also demonstrated that 10 wt% of BaMnO 3 -doped MgH 2 samples desorbed 5.36 wt% of H 2 at 300 °C within 1 h whereas milled MgH 2 only released less than 0.32 wt% of H 2. The activation energy was lowered by 45 kJ/mol compared to that of MgH 2 after the addition of 10 wt% of BaMnO 3. Further analyzed by using XRD revealed that the formation of Mg 0·9 Mn 0·1 O, Mn 3 O 4 and Ba or Ba-containing enhanced the performance of MgH 2. • BaMnO 3 -doped MgH 2 exhibited an excellent hydrogen sorption kinetics property. • MgH 2 + 10 wt% BaMnO 3 can uptake 5.22 wt% H 2 within 2 min at 250 °C under 33 atm H 2. • The desorption E A of MgH 2 + 10 wt% BaMnO 3 is reduced to 99 kJ/mol. • The improved of BaMnO 3 -doped MgH 2 due to the in-situ formation of Mg 0·9 Mn 0·1 O, Mn 3 O 4 and Ba or Ba-containing. [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]

Study on the catalytic roles of MgFe 2 O 4 on the dehydrogenation performance of LiAlH 4 was carried out for the first time. Notable improvement on the dehydrogenation of LiAlH 4 –MgFe 2 O 4 compound was observed. The initial decomposition temperatures for the catalyzed LiAlH 4 were decreased to 95 °C and 145 °C for the first and second stage reactions, which were 48 °C and 28 °C lower than the milled LiAlH 4. As for the desorption kinetics performance, the MgFe 2 O 4 doped-LiAlH 4 sample was able to desorb faster with a value of 3.5 wt% of hydrogen in 30 min (90 °C) while the undoped LiAlH 4 was only able to desorb 0.1 wt% of hydrogen. The activation energy determined from the Kissinger analysis for the first two desorption reactions were 73 kJ/mol and 97 kJ/mol; which were 31 and 17 kJ/mol lower as compared to the milled LiAlH 4. The X-ray diffraction result suggested that the MgFe 2 O 4 had promoted significant improvements by reducing the LiAlH 4 decomposition temperature and faster desorption kinetics through the formation of active species of Fe, LiFeO 2 and MgO that were formed during the heating process. • The H 2 storage properties of LiAlH 4 /MgFe 2 O 4 have been studied for the first time. • Desorption properties of LiAlH 4 are improved after adding with MgFe 2 O 4. • LiAlH 4 //MgFe 2 O 4 composite could desorb 3.5 wt% H 2 within 30 min at 90 °C. • The formation of new species of Fe, LiFeO 2 and MgO phases plays a 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]