Study of the hydrogenation mechanism of LaCuMg8 ternary phase: The decomposition induces kinetics improvement

Abstract

Kinetic and thermodynamic studyMorphologic effects a b s t r a c tThe hydrogen sorption properties of LaCuMg 8 are investigated. LaCuMg 8 crystallizes in the La 2 Mg 17 structure type with the lattice parameters a ¼ 10.1254(2) Å and c ¼ 10.0751(2) Å .An absorption mechanism in 2 steps was reported earlier: (i) the first step, which is irreversible, induces the decomposition of LaCuMg 8 into an intimate mixture of 3 phases of sub-micronic size (i.e. LaH 3 , MgCu 2 and MgH 2 ); (ii) the second step consists in the reversible absorption of the "LaCuMg 8 activated powder" with kinetics better than for pure magnesium. In order to get a better understanding of the absorption process, it was investigated from thermodynamic, kinetic and morphology points of view. From thermodynamic point of view, the "LaCuMg 8 activated powder" behaves like a mixture. Concerning the kinetics, the activation energy was evaluated at about 65 kJ/mol H 2, using AvramieErofeev model and Arrhenius law. To explain the enhancement of the kinetics, both effects of (i) Mg 2 Cu/ MgCu 2 transformation and (ii) morphology induced by the decomposition have been considered.

Effect of microwave irradiation on hydrogen sorption properties of hand mixed MgH2 – 10 wt.% carbon fibers

“…On the other hand, the average sizes of the larger magnesium particles were slightly reduced from 50 to 30 microns after several sorption cycles. A similar phenomenon was reported by S. Couillaud et al in the case of LaCuMg 8 [25]. After decomposition (hydrogenation) of LaCuMg 8 , the powder (in the range 50e200 mm) shows an irregular shape and its surface is rather smooth.…”

A high-pressure and high-temperature gas-loading system for the study of conventional to real industrial sized samples in catalysed gas/solid and liquid/solid reactions

“…These three examples, together with a study of the hydrogenation mechanism of LaCuMg 8 (Couillaud et al, 2012) and a study of the synthesis of (Mg-Ni)-based nanoconfined hydrides (Zlotea et al, 2013), illustrate the potentials of the GLS for hydrogen storage studies and for monitoring structural phase changes and in situ chemical reactions of microand nano-sized phases at high temperature and pressure.…”

An investigation of gaseous hydrogen storage characterizations of Mg–Y–Ni–Cu alloys synthesized by melt spinning

“…The improved de-/hydrogenation kinetics of ternary LaCuMg 8 alloy could be explained by the inuences of MgCu 2 and Mg 2 Cu. 32 Transition metals can play the role of catalysts to dissociate the H 2 molecule into absorbable monotonic hydrogen atoms. [33][34][35] To investigate the effects of Y content on hydrogen storage and thermodynamic and dynamic characteristics, we chose Y to partially substitute for Mg in Mg-Ni-based alloy and applied melt spinning technology to prepare nanocrystalline and amorphous Mg 25Àx Y x Ni 9 Cu (x ¼ 0-7) alloys in the present study.…”