Hydrogen storage kinetics of TiH2/ZrCl4 catalyst based on MgH2

Abstract

The introduction of TiH₂ and ZrCl₄ as synergistic catalysts significantly improves the performance of magnesium-based hydrogen storage materials in terms of kinetics. The MgH₂–4TiH₂–4ZrCl₄ composite, prepared by the mechanical ball milling, exhibits an initial hydrogen desorption temperature of 218.4 °C. This composite can absorb 4.2 wt% H₂ at 100 °C for 15 min and quickly absorb 6.4 wt% H₂ at 225 °C in just 30 s. The activation energy for hydrogen desorption is calculated to be 89.83 kJ/mol based on the kinetic curve. Hydrogen storage capacity remains at 6.8 wt% after ten cycles. Mechanistic studies reveal that Zr⁰ and Zr³⁺, generated after ball milling, cause the catalyst to adhere uniformly to the MgH₂ surface, providing additional active sites and creating more hydrogen diffusion at the MgH₂/Mg interface. TiH₂ encourages MgH₂ nucleation, with H₂ dissociation occurring on the TiH₂ surface. In addition, ZrCl₄ helps to prevent Mg/MgH₂ particles aggregation, thereby enhancing cycle stability. These demonstrate the importance of transition metal interactions with Mg/MgH₂ in enhancing hydrogen storage performance.