Effects of ball milling and TiF3 addition on the dehydrogenation temperature of Ca(BH$_{4}$)$_{2}$ polymorphs

The changes introduced by both ball milling and the addition of small amounts of TiF$_{3}$ in the kinetics of the hydrogen desorption of three different Ca(BH$_{4}$)$_{2}$ polymorphs (α, β and γ) have been systematically investigated. The samples with different polymorphic contents, before and after the addition of TiF3, were characterized by powder X-ray diffraction and vibrational spectroscopy. The hydrogen desorption reaction pathways were monitored by differential scanning calorimetry. The hydrogen desorption of Ca(BH$_{4}$)$_{2}$ depends strongly on the amount of coexistent α, β and γ polymorphs as well as additional ball milling and added TiF$_{3}$ to the sample. The addition of TiF3 increased the hydrogen desorption rate without significant dissociation of the fluoride. The combination of an α-Ca(BH$_{4}$)$_{2}$ rich sample with 10 mol% of TiF$_{3}$ and 8 h of milling led to up to 27 ∘C decrease of the hydrogen desorption peak temperature.