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 (TiVO3.5) by oxidizing a solid-solution MXene (Ti0.5V0.5)3C2 at 300 °C and its high activity as a catalyst precursor in the hydrogen storage reaction of MgH2. The prepared TiVO3.5 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 TiVO3.5 remarkably reduces the dehydrogenation and hydrogenation temperatures of MgH2 and enhances the reaction kinetics. The 10 wt% TiVO3.5-containing sample exhibits optimal hydrogen storage properties, as it desorbs approximately 5.0 wt% H2 in 10 min at 250 °C and re-absorbs 3.9 wt% H2 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 MgH2-10 wt% TiVO3.5 sample, representing a 59% reduction in comparison with pristine MgH2 (153.8 kJ/mol), which reasonably explains the remarkably reduced dehydrogenation operating temperature. Metallic Ti and V are detected after ball milling with MgH2; they are uniformly dispersed on the MgH2 matrix and act as actual catalytic species for the improvement of the hydrogen storage properties of MgH2.