Hydrogen sorption kinetics of MgH2 catalyzed with NbF5

The influence of NbF5 as an additive on the H-sorption kinetics of MgH2 was investigated. We found that the hydrogen sorption capacity and sorption kinetics of the composites were dependent on the addition amount of NbF5 as well as the milling time. Fast kinetics are obtained using 2 mol% NbF5. At 573 K, the MgH2+2 mol% NbF5 milled for 5h can absorb 5wt.% hydrogen in 12s and 6wt.% in 60 min, and desorb 4.4 wt.% in 10 min and 5 wt.% in 60 min. DSC examination indicates that the desorption temperature is reduced by 64 K, and the activation energy for hydrogen desorption is estimated to be similar to 90 kJ/mol H-2 from the Kissinger Plot, indicating that MgH2 is significantly activated due to the catalytic effect of NbF5. Furthermore, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed to characterize the structural evolution upon milling and dehydrogenation. (C) 2006 Elsevier B.V. All rights reserved.