Tunable synthesis of (Mg–Ni)-based hydrides nanoconfined in templated carbon studied by in situ synchrotron diffraction

Abstract

The formation of ultra-small Mg-based particles nanoconfined into the mesopores of a carbon template was studied by in situ synchrotron diffraction. Either Mg 2 Ni or Mg 2 NiH 4 nanoparticles can be directly formed starting from separate Ni and MgH 2 species by tuning the H 2 pressure. Both ultra-small Mg 2 Ni and Mg 2 NiH 4 nanoparticles (~4 nm) are extremely stable against coalescence during hydrogen sorption cycling and prolonged exposure to high temperature as compared to Mg and MgH 2 nanoparticles that show severe coalescence under same experimental conditions. The structural transition reported in bulk Mg 2 NiH 4 from high temperature cubic to low temperature monoclinic structure is no longer observed for the nanoconfined particles. Hydrogen absorption/desorption in nanosized Mg 2 Ni is reversible and desorption kinetics from Mg 2 NiH 4 proceeds very quickly (~5 min) even at 483 K. On the contrary, the thermodynamics properties are not altered by nanoconfinement. This study opens new routes for successful nanoconfinement of stoichiometric hydrides into the pores of carbon hosts along with a better understanding of nanochemistry.

Review of magnesium hydride-based materials: development and optimisation

“…The work of Zlotea et al [64] showed that contrary to MgH 2 , the size of the nanoparticles of Mg 2 NiH 4 is not affected by sorption cycling nor by high temperature. Indeed, Fig.…”

“…To modify the sorption properties of magnesium or magnesium alloys, the use of particle confinement [62][63][64][65] has been proposed. By increasing the surface-to-bulk atomic ratio, changes in the thermodynamics are foreseen.…”

“…Intermetallic Mg 2 Ni and its hydride Mg 2 NiH 4 nanoparticles were prepared and stabilised into the mesopores of a template carbon [64,69]. One approach was to first deposit well-defined Ni nanoparticles inside the pores, followed by vapour-phase deposition of Mg and hydrogenation.…”

Complex and liquid hydrides for energy storage

“…One of the earliest reports is on Mg 2 NiH 4 , formed by the deposition of Mg into the pores of a carbon scaffold that already contained Ni nanoparticles [135]. The resulting *4 nm Mg 2 Ni and Mg 2 NiH 4 nanoparticles were very stable upon cycling, with sorption being achieved within 5 min at 210°C [136]. Magnesium boron hydrides were prepared by the pre-deposition of Mg nanoparticles, followed by an exclusively pore-confined reaction (because of the high reactivity of the pore-confined nanoparticles) with diborane [137,138].…”

Nanosized Magnesium Electrochemically Deposited on a Carbon Nanotubes Suspension: Synthesis and Hydrogen Storage

“…In this context, the main improvements achieved so far through nanoconfinement have been in terms of hydrogen kinetics. The carbon scaffold is also expected to limit the growth of the Mg nanoparticles upon hydrogen cycling and, thus, lead to stable hydrogen kinetics (Zlotea et al, 2013). Currently, Mg nanoconfinement with carbon materials is usually done via melt infiltration or thermal decomposition of an Mg precursor initially impregnated in the porosity of the carbon scaffold (Konarova et al, 2012;Liu et al, 2014).…”