Bullet-like vanadium-based MOFs as a highly active catalyst for promoting the hydrogen storage property in MgH₂

The practical application of magnesium hydride (MgH₂) was seriously limited by its high desorption temperature and slow desorption kinetics. In this study, a bullet-like catalyst based on vanadium related MOFs (MOFs-V) was successfully synthesized and doped with MgH₂ by ball milling to improve its hydrogen storage performance. Microstructure analysis demonstrated that the as-synthesized MOFs was consisted of V₂O₃ with a bullet-like structure. After adding 7wt% MOFs-V, the initial desorption temperature of MgH₂ was reduced from 340.0 to 190.6°C. Besides, the MgH₂+7wt%MOFs-V composite released 6.4wt% H₂ within 5 min at 300°C. Hydrogen uptake was started at 60°C under 3200 kPa hydrogen pressure for the 7wt% MOFs-V containing sample. The desorption and absorption apparent activity energies of the MgH₂+7wt%MOFs-V composite were calculated to be (98.4 ± 2.9) and (30.3 ± 2.1) kJ·mol⁻¹, much lower than (157.5 ± 3.3) and (78.2 ± 3.4) kJ·mol⁻¹ for the as-prepared MgH₂. The MgH₂+7wt%MOFs-V composite exhibited superior cyclic property. During the 20 cycles isothermal dehydrogenation and hydrogenation experiments, the hydrogen storage capacity stayed almost unchanged. X-ray diffraction (XRD) and X-ray photoelectron spectrometer (XPS) measurements confirmed the presence of metallic vanadium in the MgH₂+7wt%MOFs-V composite, which served as catalytic unit to markedly improve the hydrogen storage properties of Mg/MgH₂ system.