Catalytic effect of Nb nanoparticles for improving the hydrogen storage properties of Mg-based nanocomposite

With the intention of improving the hydrogenation/dehydrogenation kinetics of Mg, Mg-7.5 wt % Nb nanocomposite has been prepared by hydrogen plasma-metal reaction approach. The spherical Nb nanoparticles (NPs) of 12 nm are uniformly decorated on the surface of Mg NPs. The Mg-Nb nanocomposite can quickly uptake 4.0 wt % H₂ in 10 min and reach a saturation value of 5.7 wt % H₂ in 60 min at 473 K. Furthermore, it can also release 4.0 wt % H₂ in 60 min at 573 K. The reversible hydrogen storage capacity is as high as 7.0 wt % at 673 K. Nb NPs transform into NbH during hydrogenation and recover after dehydrogenation process. They restrain the growth of Mg and work as catalysts to accelerate the hydrogen transportation in the Mg-based nanocomposite by decreasing the activation energies of hydrogenation/dehydrogenation to 70.9 and 86.4 kJmol^-1, respectively. The catalytic mechanism of Nb NPs is explained in terms of spillover, d-electrons and electronegativity effects. The nanosizing effects of both Mg and Nb and the catalytic effect of Nb NPs give rise to the improved hydrogen storage properties of the Mg-Nb nanocomposite at moderate temperatures.