Improvement on Hydrogen Desorption Performance of Calcium Borohydride Diammoniate Doped with Transition Metal Chlorides

Calcium borohydride diammoniate with a molecular formula of Ca(BH4)(2).2NH(3) is a novel complex hydride for hydrogen storage. However, it suffers from high temperature and sluggish kinetics for hydrogen desorption. In this work, the temperature and kinetics for hydrogen desorption of calcium borohydride diammoniate were effectively improved through doping transition metal chlorides (such as CoCl2, NiCl2, and FeCl3) in a closed vessel. Three additives could effectively decrease the temperature for hydrogen desorption of Ca(BH4)(2).2NH3. Among them, CoCl2-doped Ca(BH4)(2).2NH3 could desorb hydrogen even at a low temperature of 170 degrees C, and at 200 degrees C, 7.6 wt % hydrogen with high purity is released, which shows superior performance for hydrogen desorption than that of pristine Ca(BH4)(2).2NH(3.) For CoCl2-doped Ca(BH4)(2).2NH(3), X-ray absorption fine structure (XAFS) revealed that the improvements could be ascribed to the catalytic function of well-dispersed cobalt particles, which results in a much lower activation energy (86.1 kJ/mol) for hydrogen desorption of calcium borohydride diammoniate.