Improved hydrogen storage performance of Ca(BH4)2: a synergetic effect of porous morphology and in situ formed TiO2

Abstract

A porous Ca(BH₄)₂-based hydride, CaB₂H₇, with nano-TiO₂ introduced in situ, was successfully synthesized via mixing Ca(BH₄)₂ with Ti(OEt)₄ followed by heat treatment. The effects of the porous structure and introduction of TiO₂ on both the non-isothermal and isothermal hydrogen desorption–absorption properties of the porous system were systematically investigated. The results show significant improvements on both the kinetics and thermodynamics of hydrogen desorption–absorption of the porous CaB₂H₇–0.1TiO₂ system, compared with the dense Ca(BH₄)₂. The desorption peak temperature is reduced by more than 50 °C and sorption capacity of ca. 5 wt% H₂ is rapidly achieved below 300 °C. The porous structure was retained in the dehydrogenated products, and rapid hydrogen absorption, approximately 80% of the desorption capacity, is obtained upon heating the product, post-dehydrogenated at 300 °C for 1 h, to 350 °C at 90 bar H₂. External addition of nano-TiO₂ also enhances the hydrogen storage properties of Ca(BH₄)₂, but to a lesser extent, compared with the synergetic effect of the porous structure and the in situ formed nano-TiO₂. In addition, desorption–absorption mechanisms of the porous CaB₂H₇–0.1TiO₂ system are also proposed.