Microstructural study of the LiBH4–MgH2 reactive hydride composite with and without Ti-isopropoxide additive

Abstract

An exhaustive microstructural characterization is reported for the LiBH 4-MgH 2 reactive hydride composite (RHC) system with and without the Ti-isopropoxide additive. X-ray diffraction (XRD) with Rietveld analysis, transmission electron microscopy (TEM) coupled to energy dispersive X-ray analysis (EDX), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS) are presented in this paper as the first time for this system in all sorption steps. New data are reported regarding average crystallite and grain size, microstrain, phase formation and morphology that contribute to the understanding of the reaction mechanism and the influence of the additives on the kinetics. Microstructural effects, related to the high dispersion of titanium based additives, results in a distinct grain refinement of MgB 2 and an increase of reaction sites which causes acceleration of desorption and absorption reactions. Considerations on stability of phases under e-beam irradiation have been also reported.

Combined x-ray photoelectron spectroscopy and scanning electron microscopy studies of the LiBH4–MgH2 reactive hydride composite with and without a Ti-based additive

“…Single crystals of MgH 2 of respectively 1100 and 760 nm for M 3 and M 3−5Ti have been observed by TEM. 22 In presence of Ti-iso, the MgH 2 crystals are smaller and have, therefore, a higher surface area which is in good agreement with the higher Mg concentration at the surface found here. A significant decrease of oxygen concentration is also observed after one cycle which may be due to the heating at 350°C under 50 bar H 2 .…”

“…Detailed analysis of these two samples is given in Ref. 22. However, the distribution of the LiBH 4 phase embedding MgH 2 appears to be quite different in presence of the Ti-iso additive.…”

“…Data are compared to previous results by X-ray absorption spectroscopy ͑XAS͒, x-ray diffraction ͑XRD͒, transmission electron microscopy ͑TEM͒, selected-area electron diffraction ͑SAED͒, and electron energy loss spectroscopy ͑EELS͒ in Refs. [18][19][20][21][22]. The new results in this paper will contribute to the understanding of the reaction mechanism and the influence of the additives on the kinetics.…”

“…At the same time the additive species migrate to the bulk where they favor heterogeneous reactions at the interface of reactants. 20 Additionally a recent exhaustive microstructural characterization for the 2LiBH 4 -MgH 2 RHC system with and without the Ti-iso additive 22 has shown that microstructural effects, related to the high dispersion of titanium-based additives, result in a distinct grain refinement of MgB 2 and an increase in the number of reaction sites, causing acceleration of desorption and absorption reactions.…”

Thermodynamics of Metal Hydrides: Tailoring Reaction Enthalpies of Hydrogen Storage Materials

“…Several experiments are indicating that transition metal fluorides are among the best additives for borohydrides (Bonatto Minella et al, 2011). While for some cases the function of the transition metal part as additive is understood Deprez et al, 2010;Deprez et al, 2011), the function of F so far remained unclear. DFT calculations performed by Yin et al (Yin et al, 2008) suggest a favourable modification of hydrogen reaction enthalpy in the LiBH 4 system by substitution of the H --ion with the F --ion.…”