Multivalent-oxygen vacancy regulation via TiO₂ addition for easily activation and rapid hydrogen ab/desorption of MgSc alloy

The application of Mg-based hydrides in portable and stationary energy storage is primarily hindered by sluggish sorption kinetics and unfavorable cycle stability. Herein, an attempt is made to enhance the hydrogen storage properties of MgSc alloy by the addition of TiO₂ nanoparticles to regulate multivalent‑oxygen vacancy. The formation of Sc₂O₃ and MgTi₂O₄ phases during heat treatment act as active sites, facilitating hydrogen absorption in the initial stages. Notably, MgSc-TiO₂ demonstrates a rapid rate of de/hydrogenation. The absorption capacity in the first cycle is 6.5 wt%, and releases 6.3 wt% H₂ within just 5 min. TiO₂ doping significantly improves the kinetics and cycling stability of the hydrogen absorption and desorption reaction, achieving a reversible capacity of 6.14 wt% at 320 °C. After 10 cycles, the capacity remains 6.32 wt% without visible decay. The improvement is attributed to the solid solution effect of Sc, the multivalent of Ti, the acceleration of electron transfer by oxygen vacancies and the alleviation of volume expansion stress by MgTi₂O₄. Ti hydrides participate in the de/hydrogenation reaction. Additionally, multivalent Ti contributes to electron transfer between Mg²⁺ and H⁻, thereby weakening the stability of Mg[sbnd]H bond. Oxygen vacancies enhance the absorption of hydrogen and accelerate H atoms diffusion.