X-RAY DIFFRACTION STUDIES OF Li-BASED COMPLEX HYDRIDES AFTER PRESSURE CYCLING

X-ray diffraction studies have been performed on Li-based complex hydrides after multiple hydriding/dehydriding pressure cycles. The effects of pressure cycling are important for longterm reliability of Li-based hydrides. Commercial grade hydrogen containing low-level impurities (O2, H2O, CO/CO2) was used for this study to show the effect of cycling on hydrogen storage capacities. Equilibrium isotherms were obtained using a Sievert’s apparatus after 1, 56, 163, 500, and 1100 pressure cycles on the Li2NH-LiNH2 system to observe hydrogen capacity as a function of cycles at 255 °C. Structural studies of the products (desorbed condition) after pressure cycling showed mainly Li2NH and LiH phases and the impurity Li2O phase. Quantitative X-ray diffraction calculations showed the Li2NH phase was reduced from 79% to 13%, and the LiH phase increased from 8% to 54% after 1100 cycles. Pressure cycling results showed 2.55 wt% (~10.25 bar) and 2.9 wt% (~0.86 bar) hydrogen storage loss after 1100 cycles. Detailed results of structural behaviors and pressure-composition isotherms after multiple cycles are also presented.