Enhancing thermodynamic and kinetic properties of MgH2 by addition of the V80Ti8Cr12 alloy

The addition of hydrogen storage alloys into Mg/MgH ₂ has recently attracted attention because it can enhance the hydrogen storage properties of the material through providing high-density grain and phase boundaries, which serve as nucleation sites for new phase formation. The different hydride phases can provide a large number of H diffusion channels. However, the current technique often only improves their kinetic properties, and has little impact on their thermodynamic properties. Herein, we propose that the addition of V ₈₀Ti ₈Cr ₁₂ improves both the thermodynamic and kinetic properties of MgH ₂. The MgH ₂-V ₈₀T _i8Cr ₁₂ composite showed excellent hydrogen absorption and desorption properties, enabling dehydrogenation at 208.9 ℃. The enthalpy of hydrogen release of MgH ₂ decreases to 69.83 kJ/mol H ₂ with the addition of V ₈₀Ti ₈Cr ₁₂. In addition, the MgH ₂-V ₈₀Ti ₈Cr ₁₂ composite possesses relatively low activation energy for hydrogen desorption (102.2 kJ/mol H ₂), which is about 32 % lower than pure MgH ₂. The structural analysis indicates that the presence of grain and phase boundaries provides nucleation sites for the formation of new phases. The stresses generated at different stages of the hydrogen absorption and desorption process can lead to elastic instability. This can optimize the thermodynamic stability of the material and reduce the activation energy. Our findings provide insights into the design and development of Mg-based hydrogen storage composite materials.