Catalysis derived from three-dimensionally ordered macroporous Nb₂O₅ towards the hydrogen storage performance of magnesium hydride

A three-dimensionally ordered macroporous (3DOM) Nb₂O₅ was successfully prepared via the colloidal crystal template method, which demonstrates a significant effect in enhancing the hydrogen storage performances of MgH₂. 3DOM Nb₂O₅ presents an overall macroporous structure with a highly ordered overall arrangement and connected layers. As limiting domains influence of 3DOM structure, Nb₂O₅ nanoparticles ranging in size from 5 to 15 nm are encapsulated with the amorphous carbon layer. The MgH₂-5 wt% 3DOM Nb₂O₅ MM 30 h composite can absorb 6.35 wt% H₂ in 500 s at 175 °C and desorb 6.95 wt% H₂ in 300 s at 300 °C. The unique Nb₂O₅ 3DOM structure can provide more active sites and a larger contact area for the hydrogen ab/desorption of MgH₂. The in situ formed NbH_x can promote the dissociation and complexation of molecular hydrogen on its surface and induce the hydrogen boundary/interface diffusion along the Mg/MgH₂ interface, thus facilitating the hydrogen ab/desorption reaction of MgH₂. In addition, the binding energy transfer of Nb₂O₅ can be observed by XPS and the electron shift at the MgH₂/Nb₂O₅ interface is further confirmed by the theoretical calculations, which can weaken the Mg-H bond and induce MgH₂ to become unstable. This finding will provide ideas for the design and preparation of catalysts with special morphologies for Mg-based hydrogen storage materials.