H2 storage efficiency and sorption kinetics in composite materials

Abstract

We have prepared two different kind of composite materials for hydrogen storage and studied their H 2 storage capacity and desorption kinetics. The first composite material consists of magnesium containing transition metal nanoclusters distributed in the Mg matrix (Mg:TM): this composite material shows better H 2 desorption performances than pure Mg. This improvement is attributed to the role of the MgH 2 -TM nanocluster interface as preferential site for hexagonal Mg (h-Mg) nucleation and to the rapid formation of interconnected h-Mg domains where H diffusion during desorption occurs. The second composite material consists of LaNi 5 particles (size < 30 m) distributed in a polymeric matrix. The H 2 storage capacity is negligible at low metal content (50 wt. %) when the metal particles are completely embedded in the polymeric matrix. The H 2 storage capacity is comparable to that of the pure LaNi 5 powders at high metal content (80 wt. %) when a percolative distribution is assumed by the LaNi 5 particles: this evidence points out the role of metalmetal interfaces and of interconnected metallic networks for H transport.

Structure modification of Mg–Nb films under hydrogen sorption cycles

“…In particular, it is evident from the experimental curves (not shown here) that the Nb-doped sample (Mg-Nb5%) exhibits kinetics ten times faster than pure Mg (Mg-Nb0%). Such results have been already reported and discussed elsewhere [2,[4][5][6]9]. Fig.…”

“…[5], the presence of a Nb induced lattice contraction in the Mg (0 0 2) planes could give rise to cooperative phenomena, already observed in nano-composite systems as a consequence of the elastic interactions [11][12][13]. Therefore, the lattice strain present in the Nb-doped samples can influence the H 2 sorption kinetics before the complete lattice strain relaxation.…”

“…It is worth to note that the porous structure tends to spread by increasing the sorption cycles and the pores are always preferentially located in the regions with a high Nb particle density. This effect can be explained considering that the interface between the Nb nanoclusters and the MgH 2 acts as a preferential nucleation site for Mg in the hydride to metal phase transition [5]. Due to the local high Nb particle density, hydrogen from the dissociated hydride phase here reaches a concentration larger than the maximum H solubility in the Mg matrix.…”

“…In particular, we found that among the different TM tested, Nb results to be one of the most efficient elements in speeding up the hydrogen kinetics. In recent papers, we proposed a possible mechanism responsible of the catalytic effect of Nb clusters dispersed in a Mg matrix [5], and we also investigated the role of vacancies and vacancy clusters formation on the H 2 kinetics [6]. However, although the catalytic effects of different TMs are clearly known, the microscopic mechanisms leading to the improved sorption kinetics are not fully understood.…”

Electronic structure and properties of LaNi5 compound from first principles

“…There are many researches on the hydrogen storage capacity [1][2][3] and absorbed mechanism [4][5][6] of LaNi 5 compound, but there are few reports on the electronic strcuture and properties of LaNi 5 compound [7][8][9]. Nevertheless, these studies are not enough, and there is no report on the hardness and magnetic properties of this compound.…”