Controlling the Dehydrogenation Reaction toward Reversibility of the LiBH4-Ca(BH4)2 Eutectic System

摘要

Controlling the dehydrogenation process in a suitable reaction route by choosing the appropriate reaction conditions is crucial for a hydrogen storage system. The dehydrogenation process of the eutectic 0.68LiBH4—0.32Ca-(BH4)2 mixture was investigated by dynamic pressure-composition isotherms, X-ray diffraction, and solid-state nuclear magnetic resonance in order to determine the optimal reaction route for the dehydrogenation and to improve the hydrogen absorption reaction. In a temperature range from 330 to 450 °C, the LiBH4—Ca(BH4)2 mixture decomposes in two major steps. First, Ca(BH4)2 decomposes into CaH2, CaB6, CaB_(12)H_(12) H2, and probably amorphous boron. Second, CaH2 reacts with LiBH4 to CaB6, LiH, and H2. Li2B_(12)H_(12) has been identified as a byproduct. It was observed that the lower dehydrogenation temperature, the more CaB6 and the less [B_(12)H_(12)]~(2-) containing phases are present in the final dehydrogenation products, resulting in improved absorption performance. The temperature dependence is discussed, providing instructions to improve reversibility for potential applications and new insights into the hydrogen sorption mechanism of metal borohydrides.