N.S. Mustafa

Improved hydrogen storage properties of MgH2 by addition of Co2NiO nanoparticles

A sample of MgH2 and 10 wt% Co2NiO was prepared by the ball milling technique. The hydrogen storage properties and reaction mechanism of the sample were examined. The temperature-programmed desorption result shows that the addition of 10 wt% Co2NiO to MgH2 exhibited a lower onset desorption temperature of 300 °C, which was decreased to 117 and 70 °C compared to as-received and as-milled MgH2, respectively. The de/rehydrogenation kinetics of MgH2 + 10 wt% Co2NiO showed improvement compared to un-doped MgH2. The results of the Kissinger plot shows that the activation energy for the hydrogen desorption of MgH2 was reduced to about 65.0 and 15.0 kJ mol−1 compared to as-received and as-milled MgH2, respectively. Meanwhile, the X-ray diffraction analysis shows the formation of a new phase of Mg–Co alloy and Co1.29Ni1.71O4 after the dehydrogenation and rehydrogenation process. It is reasonable to conclude that the Co2NiO additive plays a catalytic role through the formation of active species of Mg–Co alloy and Co1.29Ni1.71O4 during the heating process, thus improving the hydrogen storage properties of MgH2.

Effect of SrFe12O19 nanopowder on the hydrogen sorption properties of MgH2

In this study, the effects of different amounts (5, 10, 15, 20 and 50 wt%) of an SrFe12O19 nanopowder, doped into MgH2 and prepared by the ball milling method, were investigated with the aim of improving hydrogen storage properties. The results indicated that 10 wt% SrFe12O19 showed the best performance, compared with un-doped MgH2, in terms of the onset dehydrogenation temperature. The desorption temperature of MgH2 + 10 wt% SrFe12O19 decreased to about 270 °C compared to the 350 °C and 420 °C for as-milled and as-received MgH2, respectively. The de/rehydrogenation kinetics of MgH2 also improved after doping with SrFe12O19. Increasing the doping amount of SrFe12O19 to 15, 20 and 50 wt% brought about negative effects, such as lower capacity and slower sorption rates. From Kissinger plot differential scanning calorimetry, the apparent activation energy was 133.31 kJ mol−1 for as-milled MgH2 and 114.22 kJ mol−1 for MgH2 + 10 wt% SrFe12O19, indicating that SrFe12O19 addition decreased the activation energy for hydrogen desorption of MgH2. From the X-ray diffraction results, it is believed that the formation of new phases of Fe, MgFe2O4 and SrO during the dehydrogenation process might be responsible for the catalytic effects which further enhanced the hydrogen storage 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.