Decomposition Behavior of Eutectic LiBH4–Mg(BH4)2 and Its Confinement Effects in Ordered Nanoporous Carbon

We present the crystal structure, diborane (B 2 H 6 ) and triborane (B 3 H n ) evolution, and dehydrogenation kinetics, of both bulk and nanoconfined Li/Mg(BH 4 ) 3  in a highly ordered nanoporous carbon template. The bialkali borohydride Li/Mg(BH 4 ) 3  mainly forms a structure similar to that of α-Mg(BH 4 ) 2 . The decomposition temperature of Li/Mg(BH 4 ) 3  lies between that of LiBH 4  and Mg(BH 4 ) 2 . A direct line-of-site residual gas analyzer mass spectrometer shows that very little diborane and no detectable triborane are released during the decomposition of bulk Li/Mg(BH 4 ) 3 , which is quite different from Mg(BH 4 ) 2  or LiBH 4 , indicating that the dual-cation borohydride undergoes a different decomposition pathway, and that the reaction pathway related to diborane or triborane formation was suppressed. The nanoconfined Li/Mg(BH 4 ) 3  shows a higher cycling capacity as well as a lower decomposition temperature but, in contrast, produces more diborane and triborane in comparison with bulk Li/Mg(BH 4 ) 3 .