This study aims at an investigation of the impurity gases emitted during the decomposition of borohydrides. For this we have set up a quantitative gas analysis based on a combination of FTIR spectroscopy and gravimetry. We show that the emission of various intermediates, in particular diborane, depends sensitively on the reaction conditions, including gas mean free path lengths, hydrogen backpressure, and sample pretreatment. Adduct-free Mg(BH 4)2 and LiBH4 emit diborane only at the impurity level, while for LiZn2(BH4)5 diborane is the main decomposition product. The decomposition reaction of LiZn 2(BH4)5 proceeds via a collision-induced dissociation of Zn(BH4)2 in Ar at ambient pressures. Various additives were tested aiming at catalyzing the decomposition of the desorbed diborane. © 2011 American Chemical Society.