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

Abstract 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. Graphical abstract Image 1 Highlights • A complex oxide TiVO 3.5 is synthesized for catalyzing hydrogen release from MgH 2. • The Ti3+ and V4+ in TiVO 3.5 are reduced to the zero-valence state after milling. • The MgH 2 -10 wt% TiVO 3.5 sample exhibits improved hydrogen storage properties. • The presence of TiVO 3.5 reduces the dehydrogenation onset temperature by 70 °C. • The dehydrogenated MgH 2 -10 wt% TiVO 3.5 sample absorbs 3.9 wt% H 2 in 5 s at 100 °C. [ABSTRACT FROM AUTHOR]