(618bh) The Effects of the Nitrogen Gas and Pressure Cycling for the Li-Based Hydrogen Storage Materials

Lithium imide/amide hydriding/de-hydriding pressure cycling has been studied to determine the hydrogen storage capacity by using different kinds of the hydrogen gases. Pressure equilibrium isotherms were obtained at 255^oC after cycling between Li₂NH <--> 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 cycling. Other results by using different kinds of gas additions to hydrogen showed the loss of the hydrogen storage capacity after cycling. 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. 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.