Solid-state magnesium-based hydrogen storage encounters challenges associated with sluggish hydrogen absorption and desorption kinetics. The incorporation of catalysts is considered a promising means to improve the hydrogen absorption and desorption kinetics of these alloys. In this experiment, we prepared the Mg 80 Ni 15 Y 5 alloy via vacuum melting and incorporated TiF 3 in varying weight percentages of 1, 3, 5, and 7 wt% through ball milling . The phase composition and microstructure of the samples were analyzed and measured using X-ray diffraction meter (XRD), Transmission Electron Microscope (TEM), Selected Area Electron Diffraction (SAED), and Scanning Electron Microscope (SEM) techniques. The results revealed that the TiF 3 introduced two catalytically phases, MgF and TiF 2 . And TiF 2 transforms into TiH 2 after hydrogen absorption, which covers the surface of MgH 2 and prolongs the nucleation time of MgH 2 .Furthermore, the addition of TiF 3 made the surface of alloy markedly coarser and more irregular and few cracks, providing channels for hydrogen diffusion. This behavior optimized the kinetic performance of the alloy. It was observed that the samples containing 7 wt%TiF 3 achieved 99.2 % hydrogen saturation even in low-temperature. It's worth mentioning that the addition of 7 wt% TiF 3 to the Mg 80 Ni 15 Y 5 alloy significantly reduced the dehydrogenation activation energy to 58.5 kJ/mol, as opposed to pure magnesium with an activation energy of 158.2 kJ/mol. This substantial reduction has effectively accelerated the hydrogen absorption and desorption rates of the alloy. However, it had only a negligible impact on the thermodynamic properties of the sample with 7 wt%TiF 3 .
We report the synergistic catalytic effects of AlH3–TiF3 composites that can improve the kinetic properties of Mg-based hydrogen storage materials. The resulting MgH2–AlH3–TiF3 composites (MA-F) exhibit 5.55 wt % reversible hydrogen storage capacity with a reduced activation energy of 100.85 kJ/mol H2. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements revealed that the in situ generated Al* reacts with TiF3 and Mg, forming Al3Ti, AlF3, and Mg17Al12 during the heating process. Al3Ti and AlF3 act as the actual catalytically active centers for the hydrogen desorption and absorption processes, accelerating the reversible conversion between Mg and MgH2. Moreover, the presence of Mg17Al12 can narrow the free energy gap between the hydrogenated and dehydrogenated states, favoring the improvement of thermodynamic properties. These discoveries demonstrate the importance of the interaction between Mg/MgH2 and transition metal composites to improve the hydrogen storage functionalities.
Ball milling the powders of Mg-based alloys with transition metal compounds is effective for improving their hydrogen storage performances. In this experiment, the alloys of La 1.7 Y 0.3 Mg 16 Ni + x wt.% TiF 3 ( x = 0–10) were prepared through mechanical milling technology. XRD , SEM , HRTEM and granulometry were used to measure the composition and microstructure of alloys. The isothermal hydrogen storage property was measured by a Sievert apparatus. The results reveal that the TiF 3 additive in ball-milled samples transforms into MgF 2 and TiH 2 after the first hydrogen absorption . Adding TiF 3 enhances the crystallinity and reduces the average particle and crystallite sizes of alloys, which is beneficial to accelerating hydriding and dehydriding kinetics. Adding 7 wt% TiF 3 into alloy decreases the dehydrogenation activation energy from 72.2 to 64.0 kJ/mol and improves the hydrogen absorption rate at low temperatures, absorbing 3.50 wt% H in 0.5 min at 323 K.
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