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

Abstract

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 °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 °C and can even absorb 1.5 wt% H₂ within 30 min at a temperature as low as 50 °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.