Enhanced hydrogen storage properties of Mg by the synergistic effect of grain refinement and NiTiO₃ nanoparticles

As a promising hydrogen storage material, the practical application of magnesium is obstructed by the stable thermodynamics and sluggish kinetics. In this paper, three kinds of NiTiO₃ catalysts with different mole ratio of Ni to Ti were successfully synthesized and doped into nanocrystalline Mg to improve its hydrogen storage properties. Experimental results indicated that all the Mg-NiTiO₃ composites showed prominent hydrogen storage performance. Especially, the Mg-NiTiO₃/TiO₂ composite could take up hydrogen at room temperature and the apparent activation energy for hydrogen absorption was dramatically decreased from 69.8 ± 1.2 (nanocrystalline Mg) kJ/mol to 34.2 ± 0.2 kJ/mol. In addition, the hydrogenated sample began to release hydrogen at about 193.2 ℃ and eventually desorbed 6.6 wt% H₂. The desorption enthalpy of the hydrogenated Mg-NiTiO₃-C was estimated to be 78.6 ± 0.8 kJ/mol, 5.3 kJ/mol lower compared to 83.9 ± 0.7 kJ/mol of nanocrystalline Mg. Besides, the sample revealed splendid cyclic stability during 20 cycles. No obvious recession occurred in the absorption and desorption kinetics and only 0.3 wt% hydrogen capacity degradation was observed. Further structural analysis demonstrates that nanosizing and catalyst doping led to a synergistic effect on the enhanced hydrogen storage performance of Mg-NiTiO₃-C composite, which might serve as a reference for future design of highly effective hydrogen storage materials.