Effect of the Partial Replacement of CaH₂ with CaF₂ in the Mixed System CaH₂ + MgB₂

Abstract

In this work the effect of a partial replacement of CaH 2 with CaF 2 on the sorption properties of the system CaH 2 + MgB 2 has been studied. The first five hydrogen absorption and four desorption reactions of the CaH 2 + MgB 2 and 3CaH 2 + CaF 2 + 4MgB 2 systems were investigated by means of volumetric measurements, high-pressure differential scanning calorimetric technique (HP-DSC), 11 B and 19 F MAS NMR spectroscopy, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD). It was observed that already during the mixing of the reactants formation of a nonstoichiometric CaF 2−x H x solid solution takes place. Formation of the CaF 2−x H x solid solution sensibly affects the overall hydrogen sorption reactions of the system CaH 2 + MgB 2 .

Complex and liquid hydrides for energy storage

“…The hydrogen release from KBH 2.8 F 1.2 takes place 433°C lower than it does in pure KBH 4 [63]. However, some of the obtained materials, specifically NaB(H 1-x F x ) 4 , appear to have relatively low thermal stability, and the released hydrogen may be contaminated with significant amounts of boron fluorides and/or borane gases and may lead to the formation of significant amounts of M 2 B 12 H 12 [64][65][66][67].…”

Structural and kinetic investigation of the hydride composite Ca(BH4)2 + MgH2 system doped with NbF5 for solid-state hydrogen storage

“…This effect could hinder the decomposition of this residual borohydride phase. The main difference concerning reaction (4a) and (5a) is the formation of the CaF 2Àx H x solid solution between CaF 2 and CaH 2 in the doped sample, as was also observed by Pistidda et al and Suarez-Alcantara et al 60,61 The value of x is determined to be 1.07, using the Rietveld method. These results also explains the change of desorption enthalpy values 42 AE 2 kJ mol À1 H 2 and 37 AE 1 kJ mol À1 H 2 for the Ca-RHC system and Ca-RHC + 0.1NbF 5 , respectively (DSC-measurements-Section 3.1).…”

A comprehensive study on lithium-based reactive hydride composite (Li-RHC) as a reversible solid-state hydrogen storage system toward potential mobile applications

“…12,19 The reaction-enthalpies of various systems were altered by using the this concept. [20][21][22][23][24][25][26][27][28][29] In this work, MgH 2 is used to stabilize the dehydrogenation products of LiBH 4 . Indeed, the overall reaction enthalpy of the LiBH 4 -MgH 2 reactive hydride composite system (Li-RHC) is reduced to 46 kJ mol À1 H 2 , 12 in comparison to the respective values of each single metal hydride (LiBH 4 (67 kJ mol À1 H 2 ), MgH 2 (75 kJ mol À1 H 2 )), 5,30 according to the following reaction path:…”