The practical applications of MgH2 as a high-density hydrogen carrier depend heavily on efficient and low-cost catalysts to accelerate the dehydriding/hydriding reactions at moderate temperatures. In the present work, this issue is addressed by synthesizing Nb-doped TiO2 solid-solution-type catalysts that dramatically improve the hydrogen sorption performances of MgH2. The catalyzed MgH2 can absorb 5 wt % of H2 even at room temperature for 20 s, release 6 wt % of H2 at 225 °C within 12 min, and the complete dehydrogenation can be achieved at 150 °C under a dynamic vacuum atmosphere. Density functional theory calculations reveal that Nb doping introduces Nb 4d orbitals with stronger interaction with H 1s into the density of states of TiO2. This considerably enhances both the adsorption and dissociation ability of the H2 molecule on the catalysts surface and the hydrogen diffusion across the specific Mg/Ti(Nb)O2 interface. The successful implementation of solid solution-type catalysts in MgH2 offers a demonstration and inspiration for the development of high-performance catalysts and solid-state hydrogen storage materials.
Keywords: Nb-doping; TiO2; catalyst; hydrogen storage materials; magnesium hydride.