Enhanced hydrogen storage properties of MgH2 with numerous hydrogen diffusion channels provided by Na2Ti3O7 nanotubes

Na2Ti3O7 nanotubes (NTs) with a uniform diameter of 10 nm and Na2Ti3O7 nanorods (NRs) with a diameter of 100-500 nm were synthesized via a hydrothermal method and a solid-state method, respectively, and then introduced into MgH2 by ball milling to catalyze the hydrogenation/dehydrogenation process. The MgH2-Na2Ti3O7 NT and MgH2-Na2Ti3O7 NR composites can desorb 6.5 wt% H2 within 6 min and 16 min at 300 degree C, respectively, while the bulk MgH2 hardly releases any hydrogen even over a much longer time. In addition, isothermal rehydrogenation measurements show that the MgH2-Na2Ti3O7 NT composite can absorb 6.0 wt% H2 within 60 s at 275 degree C and can even absorb 1.5 wt% H2 within 30 min at a temperature as low as 50 degree C. TEM and HRTEM analyses indicate that the Na2Ti3O7 NTs are homogeneously distributed in MgH2, which catalyze the de-/rehydrogenation of MgH2 and meanwhile offer numerous diffusion channels to significantly accelerate the transportation of hydrogen atoms. Moreover, compared with bulk MgH2 and the MgH2-Na2Ti3O7 NR composite, the activation energy of the MgH2-Na2Ti3O7 NT composite is significantly decreased to 70.43 kJ mol-1. Such Na2Ti3O7 NTs with a unique morphology of the catalyst being distributed as nanotubes in MgH2 are believed to pave the way for the future design of hydrogen storage materials with excellent hydrogen storage performances.