Abstract: MgH₂, as one of the typical solid-state hydrogen storage materials, has attracted extensive attention. However, the slow kinetics and poor cycle stability limit its application. In this work, LiBH₄ and YNi₅ alloy were co-added as additives to MgH₂ via ball milling, thereby realizing an excellent dehydrogenation performance and good cycle stability at 300 °C. The MgH₂-0.04LiBH₄-0.01YNi₅ composite can release 7 wt.% of hydrogen in around 10 min at 300 °C and still have a reversible hydrogen storage capacity of 6.42 wt.% after 110 cycles, with a capacity retention rate as high as 90.3 % based on the second dehydrogenation capacity. The FTIR results show that LiBH₄ can reversibly absorb and desorb hydrogen throughout the hydrogen ab/desorption process, which contributes a portion of the reversible hydrogen storage capacity to the MgH₂-0.04LiBH₄-0.01YNi₅ composite. Due to the small amount of LiBH₄ and YNi₅, the dehydrogenation activation energy of MgH₂ did not decrease significantly, nor did the dehydrogenation enthalpy (∆H) change. However, the MgNi₃B₂ and in-situ formed YH₃ during the hydrogen absorption/desorption cycles is not only beneficial to the improvement of the kinetics performance for MgH₂ but also improves its cycle stability. This work provides a straightforward method for developing high reversible hydrogen capacity on Mg-based hydrogen storage materials with moderate kinetic performance.

Key words: Hydrogen storage, Magnesium hydride, Lithium borohydride, YNi₅ alloy, High reversible capacity