Synthesis, Structures and Dehydrogenation Properties of Zinc Borohydride Ethylenediamine Complexes

Abstract

Zinc borohydride–ethylenediamine composites with high hydrogen content and moderate decomposition temperatures were synthesized by a solvent based approach in diethyl ether. The complexation with ethylenediamine allows to stabilize zinc borohydride, Zn(BH4)2, which otherwise decomposes at temperatures below RT. The crystal structures of Zn(en)n(BH4)2, n=3 or 4, were determined from synchrotron radiation powder X-ray diffraction data (SR-PXD). The decomposition mechanism of the compounds was analyzed by in situ SR-PXD and thermal analysis. Zn(en)n(BH4)2, n=3 or 4, release ethylenediamine during heating, while the composites Zn(BH4)2-en 1:2 and 1:1 release 8 or 5 wt% of hydrogen at 135 and 110 °C, respectively, in contrast to e. g. alkali metal zinc borohydrides, which release a mix of diborane and hydrogen.