Synthesis and thermal decomposition of potassium tetraamidoboranealuminate, K[Al(NH2BH3)4]

Abstract

© 2017 Hydrogen Energy Publications LLC A new potassium tetraamidoboranealuminate, K[Al(NH2BH3)4], has been synthesized by a mechanochemical reaction between KAlH4and NH3BH3. The compound, K[Al(NH2BH3)4], crystallizes in a triclinic unit cell with space group symmetry P-1. The crystal structure consists of [K(NH2BH3)6]5-octahedra which facilitate the bridging between K+in 1D chains, while also bridging K+to Al3+to connect the 1D chains in a 3D network. Thermal analysis reveals that K[Al(NH2BH3)4] decomposes in two exothermic steps at T ~ 94 and 138 °C and releases primarily hydrogen. The total gas release amounts to ~6.0 wt% H2. The decomposition products are investigated ex situ by powder X-ray diffraction, infrared spectroscopy, and11B and27Al NMR and identified as KBH4and amorphous phases, possibly BN3, N2BH, and/or NBH2whereas aluminum is found in four-, five-, and six-fold coordination. Unfortunately, the decomposed sample shows no hydrogen absorption at T = 260 °C and p(H2) = 110 bar.