New Quaternary Hydride Li$_{3}$BN$_{2}$H$_{8}$ with $>$10 wt{\%} Hydrogen: II. Hydrogen Desorption Measurements

We report thermogravimetric, volumetric, and calorimetric measurements of hydrogen desorption from the new quaternary hydride Li$_{3}$BN$_{2}$H$_{8}$ (11.9 wt{\%} theoretical hydrogen capacity). Li$_{3}$BN$_{2}$H$_{8}$ releases $\ge $10 wt{\%} hydrogen at temperatures above $\sim $250$^{\circ}$C. Simultaneous mass spectrometry residual gas analysis shows that a small amount of ammonia (2-3 mole{\%} of the generated gas) is released concurrently. Independent volumetric and gravimetric measurements are in excellent agreement regarding the quantities of hydrogen and ammonia released. Differential scanning calorimetery and in-situ x-ray diffraction show that Li$_{3}$BN$_{2}$H$_{8}$ melts at $\sim $190$^{\circ}$C, thus hydrogen evolution occurs from the molten state. It dehydrides to the solid product Li$_{3}$BN$_{2}$, and the evolved gas satisfactorily accounts for all of the available hydrogen content. Preliminary calorimetric measurements suggest that hydrogen release is exothermic, and, hence, not easily reversible; to date, rehydriding has not been achieved.