Advancement in the Hydrogen Absorbing and Releasing Kinetics of MgH2 by Mixing with Small Percentages of Zn(BH4)2 and Ni

Zn(BH₄)₂ made in our former investigation and Ni were mixed with MgH₂ to promote the hydrogen absorption and release features of Mg. A 96 w/o MgH₂ + 2 w/o Ni + 2 w/o Zn(BH₄)₂ sample [named MgH₂–4NZ] was prepared by milling in a planetary ball mill in a hydrogen atmosphere. The proportion of the additive was small (4 w/o) in order to increase hydrogen absorbing and releasing rates without majorly sacrificing the hydrogen-storage capacity. The hydrogen absorption and release features of the MgH₂–4NZ were inspected in detail and compared with those of 99 w/o MgH₂ + 1 w/o Zn(BH₄)₂ [named MgH₂–1Z] and 95 w/o MgH₂ + 2.5 w/o Ni + 2.5 w/o Zn(BH₄)₂ [named MgH₂–5NZ] samples. The activation of the MgH₂–4NZ was not required. The MgH₂–4NZ had a useful hydrogen-storage capacity (the quantity of hydrogen absorbed after 60 min) of about 5.5 w/o at the first cycle. At the first cycle, the MgH₂–4NZ absorbed 3.84 w/o hydrogen after 5 min and 5.47 w/o hydrogen after 60 min at 593 K in 12 bar hydrogen. The MgH₂–4NZ had a higher releasing rate, larger amounts of hydrogen absorbed and released after 60 min, and a better cycling capability than the MgH₂–1Z. Staying of Ni (as Mg₂Ni) and a larger amount of Zn among particles is believed to have led to the better cycling capability of the MgH₂–4NZ.