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

Abstract

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 (TiB2 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.