Abstract: The design of an excellent active catalyst to improve the sluggish kinetic and thermodynamic properties of magnesium hydride (MgH₂) remains a great challenge to achieve its practical application. In this study, a novel Ni-Nb/rGO nanocomposite catalyst was successfully prepared by one-spot hydrothermal and subsequent calcination methods. The novel Ni-Nb/rGO nanocomposite exhibits an exceptional catalytic effect on improving MgH₂ sorption properties. Specifically, the onset desorption temperature of MgH₂ + 10 wt% Ni-Nb/rGO composite is reduced to 198 °C, much lower than that of undoped MgH₂ (330 °C). Interestingly, the composite can release 5.0, 5.9, and 6.0 wt% H₂ within 10 min at 245, 260, and 275 °C, respectively. Furthermore, the dehydrogenated MgH₂ + 10 wt% Ni-Nb/rGO composite starts to absorb hydrogen even at room temperature with approximate 2.75 wt% H₂ uptake at 75 °C under 3 MPa H₂ pressure within 30 min and exhibits excellent stability by maintaining 6.0 wt% hydrogen content after 20 cycles at 300 °C. Chou's model suggests that the de/hydrogenation kinetics of Ni-Nb/rGO-modified MgH₂ switches from surface penetration model to diffusion model at lower temperatures. Additionally, the activation energies (E_a) for the de/hydrogenation of MgH₂ + 10 wt% Ni-Nb/rGO are reduced to 57.8 kJ/mol and 33.9 kJ/mol, which are significantly lower than those of undoped MgH₂. The work demonstrates that the addition of a novel ternary Ni-Nb/rGO catalyst is an effective strategy to not only boost the sorption kinetics of MgH₂ but also maintain its cycling property.

Key words: Hydrogen storage materials, Magnesium hydride, Ni-Nb/rGO, Kinetic analysis, Catalytic mechanism