Abstract
A composite material of LiAl(NH2)4 and LiH irreversibly releases H2 gas by 6.1 mass% below 130 °C. The H2 desorption mechanism of the composite has been proposed, but it is still controversial because the decomposition mechanism of LiAl(NH2)4 is not well-known. We here examined the gas desorption property of LiAl(NH2)4 by using thermogravimetry and mass spectroscopy. On heating to 160 °C, a large amount of NH3 release was observed, which was followed by mild gas emission until 500 °C. We investigated the detailed structural changes on the NH3 gas desorption by using synchrotron X-ray total scattering, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. On the basis of these structural analyses, we obtained strong evidence that the amorphous intermediate product described as LiAl(NH2)x(NH)yNz was formed during the thermal decomposition process, where the AlN4 network polymerization proceeds and the ratio of [NH2]−, [NH]2–, and [N]3– units gradually changes with releasing NH3 gas. Finally, the crystalline Li3AlN2 and the amorphous residue, which will become AlN with longer annealing, were formed because of the complete exhaustion of hydrogen atoms by NH3 desorption.
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