Raman spectroscopic observation of dehydrogenation in ball-milled LiNH2–LiBH4–MgH2 nanoparticles

In situ Raman spectroscopy was used to monitor the dehydrogenation of ball-milled mixtures of LiNH2–LiBH4–MgH2 nanoparticles. The as-milled powders were found to contain a mixture of Li4BN3H10 and Mg(NH2)2, with no evidence of residual LiNH2 or LiBH4. It was observed that the dehydrogenation of both of Li4BN3H10 and Mg(NH2)2 begins at 353 K. The Mg(NH2)2 was completely consumed by 415 K, while Li4BN3H10 persisted and continued to release hydrogen up to 453 K. At higher temperatures Li4BN3H10 melts and reacts with MgH2 to form Li2Mg(NH)2 and hydrogen gas. Cycling studies of the ball-milled mixture at 423 K and 8 MPa (80 bar) found that during rehydrogenation of Li4BN3H10 Raman spectral modes reappear, indicating partial reversal of the Li4BN3H10 to Li2Mg(NH)2 transformation.