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 H-2 pressure and temperature. Both ultra-small Mg2Ni and Mg2NiH4 nanoparticles (similar to 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 (similar to 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. (C) 2012 Elsevier Ltd. All rights reserved.