New hydrogen-rich ammonium metal borohydrides, NH4[M(BH4)4], M = Y, Sc, Al, as potential H2 sourcesThis work is dedicated to Viktor V. Struzhkin at his birthday.Electronic supplementary information (ESI) available: The additional PXD, FTIR, TGA/DSC/EGA data and Rietveld plots. See DOI: 10.1039/c7dt03926c

• Main Authors: Starobrat, A, Jaro, T, Grochala, W
• Format: Journal Article
• Language: English
• Published: 26.03.2018
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt03926c

Three metal-ammonium borohydrides, NH 4 [M(BH 4 ) 4 ] M = Y, Sc, Al, denoted 1 , 2 , 3 , respectively, were prepared via a low temperature mechanochemical synthesis and characterized using PXRD, FTIR and TGA/DSC/MS. The compounds 1 and 2 adopt the P 2 1 / c space group while the compound 3 crystallizes in an orthorhombic unit cell ( Fddd ). The first decomposition step of all three derivatives of ammonium borohydride has the maximum rate at 48 °C, 53 °C and 35 °C for 1 , 2 and 3 , respectively, which are comparable to that for NH 4 BH 4 (53 °C). The thermal decomposition of these metal-ammonium borohydrides is a multistep process, with predominantly exothermic low-temperature stages. The compound 1 decomposes via known Y(BH 4 ) 3 , however, some of the solid decomposition products of the other two compounds have not been fully identified. In the system containing compound 2 , a new, more dense polymorph of the previously reported LiSc(BH 4 ) 4 has been detected as the intermediate of slow decomposition at room temperature. Three derivatives of ammonium borohydride have been prepared and characterized in order to stabilize this second most hydrogen-rich compound.