| Popis: |
Ca(BH 4 ) 2 with 11.6 mass% hydrogen is considered a promising material for hydrogen storage applications due to its high gravimetric and volumetric capacity as well as predicted thermodynamic properties suitable for hydrogen storage purposes. However, the material displays poor reversibility, and a deeper understanding of decomposition pathway and rehydrogenation mechanisms are needed to solve this issue. In this work the rehydrogenation properties of phases present in different samples of decomposed Ca(BH 4 ) 2 were investigated. The dehydrogenated and rehydrogenated samples were characterized by Powder X-ray Diffraction (PXD) and infrared spectroscopy (IR). The results show that at least one amorphous phase is hydrogenated to form Ca(BH 4 ) 2 at relatively moderate conditions (100 bar, 305 °C) without addition of a catalyst. Bragg peaks from the earlier reported intermediate phase, CaB 2 H x , disappear during rehydrogenation. However, it cannot be confirmed from the results presented here if this is due to rehydrogenation or if CaB 2 H x is consumed in a reaction with phases formed during rehydrogenation of the amorphous phase(s). Infrared spectra show presence of amorphous decomposition products different from the earlier identified decomposition products CaH 2 , CaB 6 and CaB 12 H 12 . These phases cannot be identified due to lack of matching literature spectra, but quantitative analysis indicates presence of amorphous products less rich in boron than CaB 6 and CaB 12 H 12 . |
Full Text from ScienceDirect