Formation of CaB₆in the thermal decomposition of the hydrogen storage material Ca(BH₄)₂

Abstract

Using a combination of high resolution X-ray powder diffraction and X-ray Raman scattering spectroscopy at the B K- and Ca L2,3-edges, we analyzed the reaction products of Ca(BH4)2 after annealing at 350 °C and 400 °C under vacuum conditions. We observed the formation of nanocrystalline/amorphous CaB6 mainly and found only small contributions from amorphous B for annealing times larger than 2 h. For short annealing times of 0.5 h at 400 °C we observed neither CaB12H12 nor CaB6. The results indicate a reaction pathway in which Ca(BH4)2 decomposes to B and CaH2 and finally reacts to form CaB6. These findings confirm the potential of using Ca(BH4)2 as a hydrogen storage medium and imply the desired cycling capabilities for achieving high-density hydrogen storage materials.

Simulation of nanosizing effects in the decomposition of Ca(BH4)2 through atomistic thin film models

“…Click here to access/download;Manuscript;PaperCabh4.pdf reaction, it has been reported in several works 7,8 that the production of CaB 6 and the absence of boron derivatives in Eq. 2 seems to permit the reversibility of the reaction at moderate condition 7 . This paper is organized as follow.…”

“…Concerning the Eq. 2, the comparison between the two different decomposition pathways is quite important in light of the recent work by Sahle et al 7 . Authors sug-gest, indeed, that the temperature of the reaction can promote the formation of CaB 6 , thus making the reaction reversible.…”

“…Li(BH 4 ) and Mg(BH 4 ) 2 ), one of the most widely studied borohydride because of its high gravimetric capacity of hydrogen (≈ 11.6 wt%). [4][5][6][7][8] However, the main drawbacks for technical applications of this class of compounds is the high hydrogenation/dehydrogenation temperature due to both thermodynamic and kinetic reasons. From a thermodynamic viewpoint, for a decomposition reaction of a generic solid hydrides if a ∆S of 130 J/mol H2 is considered, which corresponds to the entropy change due to the formation of a gas (H 2 ) from a solid, it turns out that an equilibrium at room conditions (i.e.…”

Properties and Applications of Metal (M) dodecahydro-closo-dodecaborates (Mn=1,2B12H12) and Their Implications for Reversible Hydrogen Storage in the Borohydrides

“…Review of the research that has been amassed concerning the thermal dehydrogenation of Ca(BH 4 ) 2 suggests that the desorption proceeds via more than one different mechanism and is strongly influenced by the reaction conditions. In general, the findings of experimental investigations coalesce around two competing reaction pathways [82]:…”

A hard X-ray self-amplified spontaneous emission free-electron laser optimizationusing evolutionary algorithms for dedicated user applications

“…10 keV) [7]. Providing bulk-sensitive probes and not requiring vacuum conditions, it is preferred to conventional soft X-ray absorption spectroscopy (XAS) measurements (below 1 keV) for complicated sample environments such as diamond anvil cells [8], liquids [9], or samples under in situ conditions [10]. In the XRS technique with synchrotron sources, the incoming photon energy is usually scanned as the scattered photons are measured at fixed energy.…”