Nb clusters formation in Nb-doped magnesium hydride

Abstract

Extended x-ray absorption fine structure spectroscopy, x-ray diffraction and transmission electron microscopy were used to analyze the Nb coordination and clustering in Nb-doped (5 at. %) h-Mg film samples deposited by rf magnetron sputtering. Results show that the catalytic effect of the Nb doping in the H-2 absorption and desorption kinetics is connected with the formation of Nb nanoclusters dispersed in the host matrix. The H-2 desorption from beta-MgH2 is favored by local elastic stresses produced by beta-NbH0.89 clusters on the MgH2 matrix that reduces the stability of the hydride phase and by preferential paths in the nanocomposite hydride

H2 storage efficiency and sorption kinetics in composite materials

“…3 we present the H 2 desorption kinetics of pure MgH 2 and of Nb-and Fe-doped [3][4][5][6][7]. We note that the activation energy pertinent to the diffusion-controlled transformation of the doped sample is very close to the value of the activation energy for H diffusion in the h-Mg phase [10].…”

“…The first one consists on a Mg matrix containing transition metal (TM) nanoclusters dispersed in the Mg bulk: here, the second component plays its role in the catalysis of the H 2 sorption kinetics by reducing the typical H 2 sorption times by up to two orders of magnitude [3][4][5][6][7].…”

“…The second composite sample consists on LaNi 5 Polysiloxane is a class of polymeric materials available on the market which shows quite good characteristics of permeability to hydrogen gas in molecular form [9]: in the preparation of the second kind of composite material we used a self-curing acetic silicon formulation (Saratoga).…”

Modelling and proper evaluation of volumetric kinetics of hydrogen desorption by metal hydrides

“…There are several chemical/physical reasons for this delay for example, the pre-oxidation of the surface before desorption and the cracking of the oxide layer during the hydride decomposition (surface activation) [29,30] or a local elastic stress at the aeb interface, which could be reduced by dopping (of e.g. Nb atoms) [31].…”

“…A modification of the chemical structure, such as doping additives [31,33,34], can impact the thermodynamic properties resulting in an alteration of the critical a-concentration c a ≡c a and desorption/re-adsorption kinetic constants b, k consequently the Sievert's constant C s ¼ b/k and the threshold pressure p abs=des . These properties (p abs=des ; k) remain independently of the particle size [35].…”