Datensatz

Zusammenfassung

X-ray absorption spectroscopy measurements at the Sc K edge (E = 4492 eV) of metallic Sc, ScCl₃, and ScCl₃-doped NaAlH₄ are presented. After the doping process, a reduction of ScCl₃ occurs, but not to the metallic Sc(0) state. A complete reduction of Sc is observed after eight absorption/desorption cycles under hydrogen. After eight cycles, formation of a structure is observed where Sc is surrounded in the first shell by 13 Al atoms at an interatomic distance of 2.85 ± 0.02 Å. A comparative study based on XAS analysis between ScCl₃, TiCl₃, and CeCl₃ used as precursor in the doping reaction of sodium alanate indicates that other factors in addition to the reduction of the precursor to the metallic state are relevant for the hydrogen release and uptake reaction kinetics. ScCl₃ and TiCl₃ exhibit a similar behavior with the formation of intermetallic compounds, while CeCl₃ is stable under comparable experimental conditions. The formation of an intermetallic entity over the cycles is correlated to the observed decrease in the storage capacity.