Abstract: Magnesium nickel hydrides are regarded as advanced metal hydride functional materials in hydrogen storage, while it is hard to improve their dehydrogenation kinetics and ensure the air-exposure stability at the same time. Herein, a novel and efficient method was developed to prepare highly active and antioxidative bulk magnesium nickel hydrides by quenching. Differential scanning calorimetry (DSC) test shows that quenching at 280 °C can decrease the dehydrogenation peak temperature of Mg₂NiH₄ from ∼345 °C to ∼260 °C. The quenched Mg₂NiH₄ can dehydrogenate completely at 230 °C within only 250 s and at 215 °C within 1000 s, respectively. Interestingly, an obvious preferred orientation of (420) diffraction index of Mg₂NiH₄ was found after quenching treatment, which is positively correlated with the free energy of hydrogen desorption, as indicated by ab-initio simulation, thus improving the dehydrogenation performance greatly. Moreover, the quenched sample also exhibits a stable air-exposure performance. There is even a slight decrease in the dehydrogenation peak temperature after air exposure for 7 days. The results provide a novel insight into the design of bulk magnesium nickel hydrides with high activity and the analysis of the corresponding dehydrogenation mechanism.

Key words: Magnesium nickel hydride, Quench treatment, Preferred orientation, Hydrogen storage performance, Dehydrogenation mechanism