The hydrogen storage capacity was evaluated on lithium imide/amide hydriding/de-hydriding pressure cycling by using hydrogen with low level impurity gases (100 ppm O2, H2O, CH4 or N2) and industrial hydrogen (H2O~32ppm, O2~10ppm and others). Pressure equilibrium isotherms were obtained at 255oC after cycling between Li2NH and LiNH2. The results showed that the nitrogen addition both allowed more of the theoretical hydrogen capacity to be storage as well as improved the stability of the hydrides after up to 1359 cycles. X-ray diffraction data shows that more Li2NH phase (less LiH phase) is present in the desorbed hydride after cycling with the nitrogen addition than is present without. The losses in hydrogen storage capacities after pressure cycling were also determined. The results shown that after 560 pressure cycles, 100 ppm O2 in hydrogen were most detrimental (0.4 wt%H2 capacity remaining out of ~5.6 wt.%) as compared to 100 ppm H2O in hydrogen gas (2 wt%H2). It was found that 1.65 wt.% hydrogen remained after 500 cycles by using industrial hydrogen. Pressure isotherms after ~100 pressure cycles showed 3.6 and 3.3 wt%H2 capacity remained by using 100 ppm CH4 and industrial hydrogen, respectively. X-ray diffraction results of the products after pressure cycling showed mainly Li2NH and LiH phases, and the impurity Li2O phase. The phase analysis results showed the Li2NH phase reduced from 77% to 13%, and LiH phase increases from 18% to 57% after 1100 cycles. The results of the effect of the impurity gases in hydrogen showed that the N2 addition will improve the hydrogen storage capacity, and the O2 has the most detrimental effect.
See more of this Group/Topical: Topical 8: Hydrogen Production and Storage