Fabrication and hydrogen sorption behaviour of nanoparticulate MgH_2 incorporated in a porous carbon host

Abstract

Nanoparticles of MgH_2 incorporated in a mesoporous carbon aerogel demonstrated accelerated hydrogen exchange kinetics but no thermodynamic change in the equilibrium hydrogen pressure. Aerogels contained pores from <2 to ~30 nm in diameter with a peak at 13 nm in the pore size distribution. Nanoscale MgH_2 was fabricated by depositing wetting layers of nickel or copper on the aerogel surface, melting Mg into the aerogel, and hydrogenating the Mg to MgH_2. Aerogels with metal wetting layers incorporated 9–16 wt% MgH_2, while a metal free aerogel incorporated only 3.6 wt% MgH_2. The improved hydrogen sorption kinetics are due to both the aerogel limiting the maximum MgH_2 particle diameter and a catalytic effect from the Ni and Cu wetting layers. At 250 °C, MgH_2 filled Ni decorated and Cu decorated carbon aerogels released H_2 at 25 wt% h^−1 and 5.5 wt% h^−1, respectively, while a MgH_2 filled aerogel without catalyst desorbed only 2.2 wt% h^−1 (all wt% h^−1 values are with respect to MgH_2 mass). At the same temperature, MgH_2 ball milled with synthetic graphite desorbed only 0.12 wt% h^−1, which demonstrated the advantage of incorporating nanoparticles in a porous host.

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