High-load Mg₂Ni nanoparticle-carbon nanofiber composites for hydrogen storage

Herein, a simple synthesis method for Mg₂Ni composites with carbon nanofibers capable of hydrogen storage is presented. Specifically, n-butyl-sec-butyl-magnesium solution in hexane (C₈H₁₈Mg, 0.7 M) and bis-cyclopentadienyl nickel(II) (nickelocene or NiCp₂) were used as precursors for the Mg₂Ni nanoparticles. Subsequently, the nanoparticles were composited with carbon nanofibers (CNF) with high loading of Mg₂Ni of 50 wt%, 75 wt%, 90 wt%, and 100 wt%. The physicochemical characterization of the materials indicated that the size of the as-prepared Mg₂Ni nanoparticles was less than 5 nm and they were highly agglomerated due to a carbon-based binder. The best hydrogen storage values were determined to be 2.6-2.7 wt%. Among the tested materials, the composite with 75 wt% of Mg₂Ni in CNF presented the best hydrogen uptake. The pressure-composition-temperature curves indicated changes in the hydriding equilibrium pressures of the Mg₂Ni nanoparticles compared to the material with a similar composition produced using ball-milling and thermodynamic calculations. Thus, the results presented herein indicate the beneficial effect of nanosizing on hydriding reactions.