Layered MoS2-supported and metallic Ni-doped MgH2 towards enhanced hydrogen storage kinetics and cycling stability

Abstract

Mg-based hydrogen storage materials have attracted much attention due to their high hydrogen content, abundant resources, and environmental friendliness. However, the high dehydrogenation temperature, slow kinetics and poor cycling stability are limiting its practical application. This work demonstrates the improved dehydrogenation kinetics and cycling stability of MgH 2 modified by a hybrid of metallic Ni and layered MoS 2 (denoted as “Ni-MoS 2 ”) introduced by ball milling, with Ni as the catalyst for MgH 2 and MoS 2 as the support for both Ni and MgH 2 . The onset dehydrogenation temperature of MgH 2 is reduced to 198 °C, and the rehydrogenation begins at a low temperature of 50 °C. The MgH 2 + 10 wt % Ni-MoS 2 composite has a fast dehydrogenation kinetics and can release 6.1 wt % hydrogen in 10 min at a constant temperature of 300 °C, with the dehydrogenation activation energy significantly reduced from 151 to 85 kJ mol −1 . During the cycling, the reversible capacity of the composite first exhibits a gradual increase for the initial 22 cycles and then maintains at 6.1 wt % from the 23th cycle to the 50th cycle. The Ni/MoS 2 addition does not change the overall thermodynamic properties of MgH 2 but can weaken the Mg–H bonds in the local regions as evident by theoretical calculation. Microstructure studies reveal that the metallic Ni will react with MgH 2 to form Mg 2 NiH 0.3 , which can act as a hydrogen pump, while the layered MoS 2 serves as a support for the well dispersion of MgH 2 and Ni. It is believed that the synergy of Mg 2 NiH 0.3 and layered MoS 2 contributes to the significantly enhanced hydrogen storage of MgH 2 . This work provides a promising and simple strategy for enhancing the Mg-based hydrogen storage materials by combination of transition metals and layered materials introduced via simple ball milling.

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