(368a) Hydrogen Storage and Effects of Cycling On Li-Based Hydrides

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 255^oC 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.