Inclusion of CoTiO3 to ameliorate the re/dehydrogenation properties of the Mg–Na–Al system

For the first time, the MgH2–NaAlH4 (ratio 4:1) destabilized system with CoTiO3 addition has been explored. The CoTiO3-doped MgH2–NaAlH4 sample begins to dehydrogenate at 130 °C, which is declined by 40 °C compared to the undoped MgH2–NaAlH4. Moreover, the de/rehydrogenation kinetics characteristics of the CoTiO3-doped MgH2–NaAlH4 were greatly ameliorated. With the inclusion of CoTiO3, the MgH2–NaAlH4 composite absorbed 5.2 wt.% H2, higher than undoped MgH2–NaAlH4. In the context of dehydrogenation, the CoTiO3-doped MgH2–NaAlH4 sample desorbed 2.6 wt.% H2, almost doubled compared to the amount of hydrogen desorbed from the undoped MgH2–NaAlH4 sample. The activation energy obtained by the Kissinger analysis for MgH2 decomposition was significantly lower by 35.9 kJ/mol than the undoped MgH2–NaAlH4 sample. The reaction mechanism demonstrated that new phases of MgCo and AlTi3 were generated in situ during the heating process and are likely to play a substantial catalytic function and be useful in ameliorating the de/rehydrogenation properties of the destabilized MgH2–NaAlH4 system with the inclusion of CoTiO3

The effect of K2SiF6 on the MgH2 hydrogen storage properties

The catalytic effect of K2SiF6 on MgH2 was first timely studied. The MgH2 + 5 wt.% K2SiF6 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 MgH2 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 MgH2. 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, Mg2Si, MgF2 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