Synchrotron X-ray diffraction and X-ray photoelectron spectroscopy studies of NaAlH4 containing Ti–Zr hydride additives

This study investigated the synergistic effects of metallic Ti–Zr hydride used as a dopant on the crystal and electronic structures of NaAlH4. The NaAlH4 + TiZr hydride system containing ball-milled, dehydrogenated, or rehydrogenated samples was studied by synchrotron X-ray diffraction (XRD). The highest reversible hydrogen capacity of sodium alanate, catalyzed with Ti–Zr hydride as dopant, was more than 4.55 wt.% at 150 °C and 0.1 MPa. The unit-cell dimensions of NaAlH4 and Al were unchanged. The evolution of Ti and Zr chemical states in sodium alanate was studied using X-ray photoelectron spectroscopy (XPS). During ball milling, dehydrogenation, and rehydrogenation the valence state of Zr was always zero. Ti3+ and Ti0 coexisted on the surface of all three sample types.