Al and Zr addition to improve the hydrogen storage kinetics of Mg-based nanocomposites: Synergistic effects of multiphase nanocatalysts

Solid-state hydrogen storage is regarded as the key technology to develop commercial application of hydrogen energy, and Mg added with high efficiency catalysts is a promising candidate to break through the barrier of hydrogen storage materials. Herein, Mg−Al and Mg−Al−Zr nanocomposites have been prepared by adding the single-metal (Al) and bimetal (Al, Zr) into Mg nanoparticles by the hydrogen plasma-metal reaction (HPMR) method. The two kinds of nanocomposites have an approximate size of 100 nm. With the expansion of the plasma current, the content of Al and Zr in Mg−Al−Zr nanocomposites increases gradually, and the addition of Al and Zr conspicuously accelerates the kinetics of hydrogen absorption and desorption of Mg. Compared with the nanocomposites with the single-metal (Al), the addition of bimetal (Al, Zr) can further enhance the hydrogen absorption kinetics of Mg, and the content of Zr has a positive effect on the reduction of activation energy (Ea). The Ea of Mg_88.3Al_7.6Zr_4.1 for hydrogen absorption is 68.6 kJ/mol, which is significantly lower than that of Mg_92.6Al_7.4 (80.6 kJ/mol) and other two Mg−Al−Zr nanocomposites with low Al and Zr (70.7 and 69.8 kJ/mol, respectively). Both the nanostructure of Mg and the synergistic catalytic effects of active “catalytic sites” and H “diffusion channels” provided by the multiphase nanocatalysts of MgAl and AlZr₃ contribute to the reduction of Ea. This work provides guidance for the development of Mg-based hydrogen storage materials with high catalytic efficiency.