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

We present the crystal structure, diborane (B2H6) and triborane (B3Hn) evolution, and dehydrogenation kinetics, of both bulk and nanoconfined Li/Mg(BH4)(3) in a highly ordered nanoporous carbon template. The bialkali borohydride Li/Mg(BH4)(3) mainly forms a structure similar to that of a-Mg(BH4)(2). The decomposition temperature of Li/Mg(BH4)(3) lies between that of LiBH4 and Mg(BH4)(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(BH4)(3), which is quite different from Mg(BH4)(2) or LiBH4, 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(BH4)(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(BH4)(3).