High-pressure synthesis, crystal structure and cyclability of the Mg2NiH4 hydride

Reactive Hydride Composite of Mg2NiH4 with Borohydrides Eutectic Mixtures

“…The results obtained in this work for the Mg 2 NiH 4 and the Mg 2 NiH 4 -LiBH 4 (MgNiLi) system are in good agreement with previous studies reported in the literature [3,7,27]. Mg 2 NiH 4 releases hydrogen under 2.7 bar of H 2 at relatively high temperature (T peak = 372 • C) and it is partially hydrogenated to Mg 2 NiH 0.3 on cooling.…”

“…In the 2nd cycle ( Figure 2b, 2nd cycle), after the polymorphic transition of LiBH 4 , also the polymorphic phase transition of Mg 2 NiH 4 is observed as a broad peak around 245 • C. Both DSC signals can be observed also on cooling. Furthermore, in the 3rd cycle ( Figure 2b, 3rd cycle), after the polymorphic transition peaks, the melting of LiBH 4 can be detected at T peak = 279 • C. All transitions are reversible and well visible during the cooling process and temperature values are in good agreement with the literature [3,4,35]. In the 4th cycle ( Figure 2b, 4th cycle), after the polymorphic transition peaks and LiBH 4 melting, at T peak = 308 • C a broad endothermic peak due to hydrogen release from LiBH 4 can be observed under 2.7 bar H 2 .…”

“…This transition is reversible, as clearly shown by the exothermic peak upon cooling at Tpeak = 234 °C, due to the cubic high temperature phase forming LT1 and LT2 [3,4]. In the 2nd cycle ( Figure 1b, 2nd cycle), the polymorphic transition is observed again and upon further heating an endothermic peak related to hydrogen release can be detected.…”

“…In order to reduce their thermodynamic stabilities, transition metals have been added to form complex metal hydrides [2], such as in the case of MgH 2 mixed with Ni to form Mg 2 NiH 4 , with a theoretical hydrogen content equal to 3.6% wt. This complex metal hydride, upon heating, shows a polymorphic transition from a monoclinic to a cubic structure at 244 • C, together with the release of one hydrogen to form Mg 2 NiH 3 [3,4]. The main dehydrogenation reaction occurs at 305 • C under 5%H 2 /95%N 2 flow or 1 bar H 2 [3,5].…”

“…This complex metal hydride, upon heating, shows a polymorphic transition from a monoclinic to a cubic structure at 244 • C, together with the release of one hydrogen to form Mg 2 NiH 3 [3,4]. The main dehydrogenation reaction occurs at 305 • C under 5%H 2 /95%N 2 flow or 1 bar H 2 [3,5]. The thermodynamic properties of the Mg-Ni-H ternary system were assessed by Zeng et al [6], where the values of temperature of decomposition as a function of hydrogen pressure are reported.…”