F.A. Halim Yap

A study on the effects of K2ZrF6 as an additive on the microstructure and hydrogen storage properties of MgH2

In this work, the hydrogenation properties of MgH2-doped K2ZrF6 with X wt% (X = 5, 10, 15 and 20) have been investigated for the first time. Analysis indicated that MgH2 doped with 10 wt% K2ZrF6 is the best composite for the improvement of the hydrogen storage properties of MgH2. The results showed that the onset desorption temperature after the addition of 10 wt% K2ZrF6 was 250 °C, which experienced the reduction of 100 °C and 200 °C from 350 °C and 450 °C for as-milled and as-received MgH2, respectively. The re/dehydrogenation kinetics also significantly improved compared to the un-doped MgH2. The results of the Arrhenius plot exhibited that the activation energy for the hydrogen desorption of MgH2 was reduced from 164 kJ mol−1 to 80 kJ mol−1 after the addition of 10 wt% K2ZrF6. Moreover, the X-ray diffraction spectra displayed the formation of new phases of KH and ZrH2 by the doping of K2ZrF6 with MgH2 after the dehydrogenation and rehydrogenation processes. These two compounds are believed to act as the active species and play a catalytic role in improving the hydrogen storage properties. It is, therefore, concluded that this newly developed catalytic doping system works well in improving the hydrogen sorption properties of MgH2.

Nanolayer-like-shaped MgFe2O4 synthesised via a simple hydrothermal method and its catalytic effect on the hydrogen storage properties of MgH2

In this study, the effect of nanolayer-like-shaped MgFe2O4 that is synthesised via a simple hydrothermal method on the performance of MgH2 for hydrogen storage is studied. MgH2 + 10 wt% MgFe2O4 is prepared by using the ball milling method. The MgFe2O4-doped MgH2 sample started to release H2 at approximately 250 °C, 90 °C and 170 °C lower than the milled and pure MgH2 respectively. At 320 °C, the isothermal desorption kinetic study has shown that the doped sample has desorbed approximately 4.8 wt% H2 in 10 min while the milled MgH2 desorbed less than 1.0 wt% H2. For isothermal absorption kinetics, the doped sample can absorb approximately 5.5 wt% H2 in 10 min at 200 °C. Meanwhile, the undoped sample absorbs only 4.0 wt% H2 in the same condition. The activation energy of 10 wt% MgFe2O4-doped MgH2 composite is 99.9 kJ mol−1, which shows a reduction of 33.1 kJ mol−1 compared to the milled MgH2 (133.0 kJ mol−1). X-ray diffraction spectra display the formation of new species which are Fe and MgO after dehydrogenation, and these new species are believed to act as the real catalyst that plays a crucial role in improving the sorption performance of the MgFe2O4-doped MgH2 system by providing a synergetic catalytic effect.