Thermal Decomposition of Mn(BH4)2–M(BH4)x and Mn(BH4)2–MHx Composites with M = Li, Na, Mg, and Ca

Abstract

The aim of this study is to investigate the thermal decomposition and hydrogen release of salt-free manganese borohydride composites with metal hydrides and metal borohydrides of lithium, sodium, magnesium, and calcium. Combined thermogravimetry, differential scanning calorimetry, and mass spectrometry were performed to measure and analyze the released gas; in situ synchrotron radiation powder X-ray diffraction was employed to investigate the reaction mechanisms. A new high-pressure polymorph of Mn(BH4)2, denoted δ-Mn(BH4)2, was prepared by ball milling of the halide free borohydrides in the composites Mn(BH4)2–M(BH4)x for M = Li and Na. In the reactive hydride composites, Mn(BH4)2–MHx (M = Li, Na, Mg, Ca), the formation of the more stable M(BH4)x for M = Li, Na, and Ca suppresses the release of diborane and provides higher hydrogen contents in the released gas during the decomposition.