Enhanced hydrogen uptake/release in 2LiH–MgB2 composite with titanium additives

The influence of different titanium additives on hydrogen sorption in LiH-MgB2 system has been investigated. For all the composites LiH-MgB2-X (X = TiF4, TiO2, TiN, and TiC), prepared by ball-milling in molar ratios 2:1:0.1, five hydrogen uptake/release cycles were performed. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and attenuated total reflection infrared spectroscopy (ATR-IR) have been used to characterize crystal phases developed during the hydrogen absorption-desorption cycles. All the composites with the titanium additives displayed an improvement of reaction kinetics, especially during hydrogen desorption. The LiH-MgB2-TiO2 system reached a storage of about 7.6 wt % H2 in ∼1.8 h for absorption and ∼2.7 h for desorption. Using in-situ SR-PXD measurements, magnesium was detected as an intermediate phase during hydrogen desorption for all composites. In the composite with TiF4 addition the formation of new phases (TiB 2 and LiF) were observed. Characteristic diffraction peaks of TiO2, TiN and TiC additives were always present during hydrogen absorption-desorption. For all as-milled composites, ATR-IR spectra did not show any signals for borohydrides, while for all hydrogenated composites B-H stretching (2450-2150 cm-1) and B-H bending (1350-1000 cm -1) bands were exactly the same as for commercial LiBH4.