A novel complex oxide TiVO3.5 as a highly active catalytic precursor for improving the hydrogen storage properties of MgH2

Herein, we demonstrate the successful preparation of a novel complex transition metal oxide (TiVO 3.5 ) by oxidizing a solid-solution MXene (Ti 0.5 V 0.5 ) 3 C 2 at 300 °C and its high activity as a catalyst precursor in the hydrogen storage reaction of MgH 2 . The prepared TiVO 3.5 inherits the layered morphology of its MXene precursor, but the layer surface becomes very coarse because of the presence of numerous nanoparticles . Adding a minor amount of TiVO 3.5 remarkably reduces the dehydrogenation and hydrogenation temperatures of MgH 2 and enhances the reaction kinetics. The 10 wt% TiVO 3.5 -containing sample exhibits optimal hydrogen storage properties, as it desorbs approximately 5.0 wt% H 2 in 10 min at 250 °C and re-absorbs 3.9 wt% H 2 in 5 s at 100 °C and under 50 bar of hydrogen pressure. The apparent activation energy is calculated to be approximately 62.4 kJ/mol for the MgH 2 -10 wt% TiVO 3.5 sample, representing a 59% reduction in comparison with pristine MgH 2 (153.8 kJ/mol), which reasonably explains the remarkably reduced dehydrogenation operating temperature. Metallic Ti and V are detected after ball milling with MgH 2 ; they are uniformly dispersed on the MgH 2 matrix and act as actual catalytic species for the improvement of the hydrogen storage properties of MgH 2 .