Remarkable enhancement and electronic mechanism for hydrogen storage kinetics of Mg nano-composite by a multi-valence Co-based catalyst

Transition metals are the traditional catalysts to improve the hydrogen storage performance of Mg. In the present article, the multi-valence Co catalyst (Co@CNTs) is prepared to improve the kinetics of Mg. The dehydrogenation temperature decreases, and desorption kinetics of MgH 2 is significantly enhanced by the addition of the catalyst. The dehydrogenation of MgH 2 –Co@CNTs composite is a random bulk nucleation/surface and three-dimensional growth with constant interface velocity reaction. Although the dehydrogenation activation energy of MgH 2 –Co@CNTs composite is reduced, the enthalpy change and entropy change of the composite are similar to the raw MgH 2 , which means the dehydrogenation is mainly dissociation of MgH 2 . Besides, the cycle performance of MgH 2 –Co@CNTs composite is stable. The damping of the performance for the composite is negligible after 50 cycles, which benefits from the in-site formed Co 3 MgC 0.5 in the composite. The Co 3 MgC 0.5 can act as a ‘hydrogen pump’ to adjust the hydrogen storage performance of Mg. Theoretical studies show that multi-valence Co can trap H 2 molecules and weaken their σ-bonds. In the first cycle, the bridging effect of Co plays an important role in the improvement of H 2 dissociation and release. In the subsequent cycles, Co 6 C 1 becomes the active site to assist the hydrogenation and dehydrogenation of the composite.