Hydrogen storage of Mg–Zn mixed metal borohydrides

On the basis of DFT results on the ideal amount of Zn required to dissolute into the α-phase of Mg(BH4)2 (space group P6122) and experimental results recently presented in the literature, mixtures of α-Mg(BH4)2 and ZnCl2 have been prepared by ball-milling, reactive milling and cryo-milling in Mg:Zn starting ratios of 1:0.33, 1:0.2 and 1:0.1. Samples have been characterized with different experimental techniques (PXD, TGA, TPD with RGA and desorption kinetics in a Sieverts apparatus). All the as-milled samples exhibited a H2 release beginning approximately at 125 °C, indicating a significant decrease in the decomposition temperature compared to pure Mg(BH4)2. With the exception of the Mg(BH4)2-0.33ZnCl2 sample ball-milled under 1 bar Ar for 3 h that showed a small B2H6 release around 120 °C, all samples are free of B2H6 emissions. Results from desorption kinetics at 195 °C suggest a strong relation between the amount of ZnCl2 in the starting mixture and the weight loss.