Effect of Carbonized 2-Methylnaphthalene on the Hydrogen Storage Performance of MgH2

Mg-based hydride materials (MgH2) are in the spotlight of hydrogen storage due to their high gravimetric density. Yet, its large-scale utilization is limited by the poor thermodynamic stability and slow kinetics. Herein, we report a novel and straightforward way to prepare MgH2 with amorphous carbon by cosintering 2-methylnaphthalene (CMN) organics with pure Mg and a hydriding combustion synthesis method, where the amorphous carbon formed from the CMN not only improves the dehydrogenation/hydrogenation capacity but also enhances the kinetics of the Mg/MgH2 system. The dehydrogenation capacity of the CMN-MgH2 composite reaches 4.88 wt % of H-2 at 623 K, nearly 2 times of pure MgH2, and its onset dehydrogenation temperature decreases to 560 K, 90 K lower than that of pure MgH2; in addition, at a lower temperature of 473 K, the composite remarkably absorbs 4.54 wt % of H-2 within 42 s while the absorption is only 0.71 wt % H-2 for the pure MgH2. Moreover, the activation energy greatly decreases from 165.35 to 101.52 kJ/mol. Further research reveals that the evolution of hydrogenation changes from a three-dimensional diffusion process to a one-dimensional diffusion process, attributed to the formation of the amorphous carbon. This work is expected to provide inspiration to design and prepare effective additives for the improvement of hydrogen storage performance of Mg-based hydrides.