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 MgH2 modified by a hybrid of metallic Ni and layered MoS2 (denoted as “Ni-MoS2”) introduced by ball milling, with Ni as the catalyst for MgH2 and MoS2 as the support for both Ni and MgH2. The onset dehydrogenation temperature of MgH2 is reduced to 198 °C, and the rehydrogenation begins at a low temperature of 50 °C. The MgH2 + 10 wt % Ni-MoS2 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/MoS2 addition does not change the overall thermodynamic properties of MgH2 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 MgH2 to form Mg2NiH0.3, which can act as a hydrogen pump, while the layered MoS2 serves as a support for the well dispersion of MgH2 and Ni. It is believed that the synergy of Mg2NiH0.3 and layered MoS2 contributes to the significantly enhanced hydrogen storage of MgH2. 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.