Microstructural and Kinetic Investigation of Hydrogen Sorption Reaction of MgH₂/Nb₂O₅Nanopowders

Abstract

MgH 2 /Nb 2 O 5 composite is one of the most promising candidates for the hydrogen delivery. The performances of these materials are usually improved by mechanical milling because a finer distribution of the catalyst and the induction of defects on the particles accelerate the hydrogen sorption kinetic of the powders. Aiming at elucidating the factors responsible for this improvement, the effect on the reaction kinetics induced by nanometric and micrometric Nb 2 O 5 powders has been investigated by a Sievert type apparatus. Nanometric additive imparts excellent performances in comparison to the micrometric one. The activation of the sample by sorption cycling has been investigated. In order to elucidate the role of the catalyst, a metallographic study of partially desorbed MgH 2 /Nb 2 O 5 composite has been applied for the first time. The powders have been also characterized by X-ray diffraction and thermal gravimetric analysis.

Review of magnesium hydride-based materials: development and optimisation

“…Previous studies reveal sample activation and improved kinetics for hydrogen release and uptake in the MgH 2 -Nb 2 O 5 system upon cycling at T = 300°C [103]. The results presented here suggest that Nb 2 O 5 reacts with Mg and forms a ternary solid solution Mg 0.60 Nb 0.40 O, which can be stabilised by relatively mild ball milling conditions and moderate working temperature, T B 300°C.…”

MgH2–Nb2O5 investigated by in situ synchrotron X-ray diffraction

“…Previous studies reveal sample activation and improved kinetics for hydrogen release and uptake in the MgH 2 ÀNb 2 O 5 system upon cycling at T ¼ 300 C [47]. The results presented here suggest that Nb 2 O 5 reacts with Mg and form a ternary solid solution Mg 0.60 Nb 0.40 O, which can be stabilized by relatively mild ball milling conditions and moderate working temperature, T 300 C. We anticipate that the reactions observed here at higher temperatures (>300 C) may also occur at lower temperatures, e.g.…”

The influence of mechanical milling parameters on hydrogen desorption from Mgh2-Wo3 composites

“…It has been argued that the addition of TMO can assist the dissociation/recombination of hydrogen on magnesium surface and therefore improve H sorption in magnesium [69,[73][74][75]. In fact, WO 3 is an efficient process control agent which creates crystal defects, lattice distortion, increase of specific surface area, increase of active sorption sites density and reduction of the effective diffusion length for sorption (by a decrease of the average interparticle distance) [43,76]. The shape analysis of TPD spectra leads to several additional conclusions.…”