Dehydriding Process and Hydrogen–Deuterium Exchange of LiBH 4 –Mg 2 FeD 6 Composites

The dehydriding process and hydrogen–deuterium exchange (H–D exchange) of x LiBH 4 + (1 − x )Mg 2 FeD 6 ( x = 0.25, 0.75) composites has been studied in detail. For the composition with x = 0.25, only one overlapping mass peak of all hydrogen and deuterium related species was observed in mass spectrometry. This implied the simultaneous dehydriding of LiBH 4 and Mg 2 FeD 6 , despite an almost 190 °C difference in the dehydriding temperatures of the respective discrete complex hydrides. In situ infrared spectroscopy measurements indicated that H–D exchange between [BH 4 ] − and [FeD 6 ] 4− had occurred during ball-milling and was promoted upon heating. The extent of H–D exchange was estimated from the areas of the relevant mass signals: immediately prior to the dehydriding, more than two H atoms in [BH 4 ] − was replaced by D atoms. For x = 0.75, H–D exchange also occurred and about one to two H atoms in [BH 4 ] − was replaced by D atoms immediately before the dehydriding. In contrast to the situation for x = 0.25, firstly LiBH 4 and Mg 2 FeD 6 dehydrided simultaneously with a special molar ratio = 1:1 at x = 0.75, and then the remaining LiBH 4 reacted with the Mg and Fe derived from the dehydriding of Mg 2 FeD 6 .