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 degrees C. Besides, the MgH2+7wt%MOFs-V composite released 6.4wt% H-2 within 5 min at 300 degrees C. Hydrogen uptake was started at 60 degrees 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 center dot mol(-1), much lower than (157.5 +/- 3.3) and (78.2 +/- 3.4) kJ center dot 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.