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

The formation of ultra-small Mg-based particles nanoconfined into the mesopores of a carbon template was studied by in situ synchrotron diffraction. Either Mg2Ni or Mg2NiH4 nanoparticles can be directly formed starting from separate Ni and MgH2 nano-species by tuning the H2 pressure and temperature. Both ultra-small Mg2Ni and Mg2NiH4 nanoparticles (∼4 nm) are extremely stable against coalescence during hydrogen sorption cycling and prolonged exposure to high temperature as compared to Mg and MgH2 nanoparticles that show severe coalescence under same experimental conditions. The structural transition reported in bulk Mg2NiH4 from high temperature cubic to low temperature monoclinic structure is no longer observed for the nanoconfined particles. Hydrogen absorption/desorption in nanosized Mg2Ni is reversible and sorption kinetics proceed 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 the underlying nanochemistry.

Graphical AbstractFigure optionsDownload as PowerPoint slideHighlights
► Mg2NiH4/Mg2Ni nanoparticles are synthesized and nanoconfined into an ordered carbon template.
► The synthetic reaction is studied by in situ synchrotron diffraction.
► Hydrogen absorption/desorption is reversible in nanoconfined Mg2NiH4.
► Sorption kinetics proceed very quickly (∼5 min) at 483–523  K.
► Mg2NiH4/Mg2Ni nanoparticles (∼4 nm) are extremely stable against coalescence during cycling.