A MOF derived multi-phase FeNi3-S catalyst for efficient hydrogen storage in magnesium hydride

Magnesium hydride (MgH 2 ) demonstrates immense potential as a solid-state hydrogen storage material, while its commercial utilization is impeded by the elevated operating temperature and sluggish reaction kinetics. Herein, a MOF derived multi-phase FeNi 3 -S catalyst was specially designed for efficient hydrogen storage in MgH 2 . Experiments confirmed that the incorporation of FeNi 3 -S into MgH 2 significantly lowered the desorption temperature and accelerated the kinetics of hydrogen desorption and reabsorption. The initial dehydrogenation temperature of the MgH 2 + 10 wt% FeNi 3 -S composite was 202 °C, which was 123 °C lower than that of pure MgH 2 . At 325 °C, the MgH 2 + 10 wt% FeNi 3 -S composite released 6.57 wt% H 2 (fully dehydrogenated) within 1000 s. Remarkably, MgH 2 + 10 wt% FeNi 3 -S composite initiated rehydrogenation at room temperature and rapidly absorbed 2.49 wt% H 2 within 30 min at 100 °C. Moreover, 6.3 wt% H 2 was still retained after 20 cycles at 300 °C, demonstrating the superior cycling performance of the MgH 2 + 10 wt% FeNi 3 -S composite. The activation energy fitting calculations further evidenced the addition of FeNi 3 -S enhanced the de/resorption kinetics of MgH 2 ( E a = 98.6 kJ/mol and 43.3 kJ/mol, respectively). Through phase and microstructural analysis, it was determined that the exceptional hydrogen storage performance of the composite was attributed to the in-situ formation of Mg/Mg 2 Ni + Fe/MgS and MgH 2 /Mg 2 NiH 4 + Fe/MgS hydrogen storage systems. Further mechanistic analysis revealed that Mg 2 Ni/Mg 2 NiH 4 served as “hydrogen pump” and Fe/MgS served as “hydrogen diffusion channel”, thus accelerating the dissociation and recombination of hydrogen molecules. In conclusion, this work offers insight into catalysts combining transition metal alloys and transition metal sulfide for exerting muti-phase synergistic effect on boosting the dehydrogenation/hydrogenation reactions of MgH 2 , which can also inspire future pioneering work on designing and fabricating high efficient catalysts in other energy storage related areas. The MOF-derived FeNi 3 alloy/FeNi sulfides nanoflower catalyst acted as both a hydrogen pump and a hydrogen diffusion channel to synergistically improve the thermodynamic and kinetic performance of MgH 2 .