Remarkably Improved Hydrogen Storage Performance of MgH2 Catalyzed by Multivalence NbHx Nanoparticles

Magnesium hydride is widely investigated because of its high hydrogen storage capacity. However, the unfavorable thermodynamic and kinetic barriers hinder its practical application. To ease these problems, three kinds of NbHx nanoparticles were prepared by wet-chemical methods and then introduced into MgH2 for catalytically enhancing its hydrogen storage properties in this work. The results show that all the NbHx nanoparticles are effective in promoting the de-/rehydrogenation kinetics of MgH2, and the three NbHx doped MgH2 composites can desorb 7.0 wt % H-2 within 9 min at 300 degrees C while ball milled MgH2 only releases 0.2 wt % H-2 in 9 min and 4.1 wt % H-2 even in 200 min. Interestingly, the significant hydrogen absorption by NbHx doped MgH2 under lower temperature ranging from 50 to 100 degrees C was observed; thus, MgH2/c-NbHx sample can uptake about 4.0 wt % H-2 at 100 degrees C. It is found that the more disordered the structure and smaller the size of the NbHx particles, the better is the catalytic effect on hydrogen storage performances of MgH2. Analyses of XRD, XPS, and TEM results indicate that the NbHx remains stable in the ball milling and following de-/rehydrogenation process and act as active catalytic species in improving hydrogen storage performance of MgH2. Moreover, a mechanism is proposed to understand how the nanosized NbHx acted as charge transfer between Mg2+ and H-, which contributes to the significantly improved hydrogen storage performances of MgH2. It is believed that the use of Nb-based nanoparticles as catalysts would greatly promote the development of the practical applications of MgH2 for hydrogen storage.