Significant Thermodynamic Destabilization and Superior Hydrogen Storage Properties of Nanocrystalline Mg-20 wt % Ti–Cr–Vx (x = 0.4, 0.6, 0.8; Ti/Cr = 2:3) Composites Synthesized by Reactive Ball Milling

Abstract

Nanocrystalline Mg-20 wt % Ti–Cr–Vx (x = 0.4, 0.6, 0.8; Ti/Cr = 2:3) composites were synthesized by reactive ball milling of Mg and Ti–Cr–Vx powders for 8 h under 5.0 MPa H2 at room temperature. The morphology, crystal structure, and isothermal hydrogen ab-/desorption properties of the materials were investigated. The as-synthesized nanocomposites comprise β-MgH2, γ-MgH2, and Ti–Cr–Vx–Hy (1.88 < y < 1.92) as confirmed by X-ray diffraction analysis. High-resolution transmission electron microscopy images show that both β-MgH2 and γ-MgH2 co-existed in a single nanocrystalline. Differential scanning calorimetry results reveal that Mg-20 wt % Ti0.16Cr0.24V0.6 powders possess the lowest hydrogen desorption temperature at 224 °C with the apparent activation energy of 76.32 kJ/mol for dehydrogenation. The nanocrystalline Mg-20 wt % Ti0.16Cr0.24V0.6 powders exhibit excellent dehydrogenation kinetics. They can desorb 5.67 wt % H2 in 20 min at 270 °C under 0.01 MPa H2 pressure, compared with only 0.10 wt % H2 for a...