Effect of Nb₂O₅ and SWCNT on the H₂ sorption properties of Mg-based hydrogen storage system

Metal hydrides are of considerable interest for safe and practical hydrogen storage. Among theses, Mg is regarded as a promising hydrogen storage material due to its high theoretical gravimetric, volumetric capacity and the full reversibility of its sorption reactions combined with low cost, low density and environmental friendliness. In previous studies, the superior catalytic effect of Nb₂O₅ was demonstrated and compared to other metal oxide catalysts. However, the nanocrystalline MgH₂-Nb₂O₅ mixtures must be milled for more than 20 hours to obtain the outstanding sorption kinetics. Long milling time causes high production costs, and makes the system less attractive for commercial applications. In this way, ternary mixtures Mg-Nb₂O₅-SWCNT (molar ratio %=97.5:0.5:2.0) were prepared by high-energy ball milling and their hydrogen storage behaviors were investigated. The structural and phase evolution of SWCNT and Nb₂O₅ were investigated by using X-ray diffractometry (XRD) and morphology by scanning electron microscopy (SEM). Detail sorption mechanisms were discussed to understand the catalytic effect.