Preferred orientation induced high efficiency dehydrogenation of metal hydrides

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.