Room Temperature Hydrogen Absorption of V2O5 Catalyzed MgH2/Mg

Magnesium hydride is a promising hydrogen storage material due to its high hydrogen storage capacity, low cost and abundance. The gravimetric and volumetric hydrogen capacities of MgH2 are about 7.6% and 110 g/L, respectively. However, its sluggish de/re-hydrogenation rates and high operating temperatures ranging between 300-400 degrees C restrict it in practical applications. Catalyzing has been proved to be an effective method to improve its hydrogen storage performance. In this work, V2O5 has been chosen as a catalyst for improving the de/re-hydrogenation kinetics of MgH2. Experimental results show that MgH2 doping with V2O5 (w= 5%) has the best hydrogen storage properties among the doping amounts (w) of 2.5% to 10%. Comparing with the pristine MgH2, the addition of V2O5 (w=5%) significantly improves the ab/desorption behaviors of MgH2. V2O5 (w=5%) doped MgH2 starts releasing hydrogen from 175 degrees C which is 89 degrees C lower than the additive-free as-milled MgH2. It should be noted that the dehydrogenated V2O5 (w=5%) doped MgH2, is able to absorb 2.1% and 3.8% in the mass fraction of H-2 respectivity, within 30 and 180 min at room temperature and 3 MPa hydrogen pressure. Under the same hydrogen pressure, when the temperature is increased to 300 degrees C, the mass fraction of H-2 absorbed by the sample is as high as 6.7% within 1 min. In addition, the catalyzed system shows a good reversibility, after 20 cycles, the hydrogen capacity maintains above 6.0%. Compared with the pure MgH2, the dehydrogenation apparent activation energy of V2O5 catalyzed sample decreased from 108 to 56 KJ.mol(-1). X-Ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been employed to investigate its reaction mechanism. It shows that the formation of metallic vanadium and low-oxidation vanadium during ball milling and dehydrogenation process play important roles in improving the de/re-hydrogenation kinetics of MgH2/Mg system.