Chemical state and local structure around titanium atoms in NaAlH4 doped with TiCl3 using X-ray absorption spectroscopy

X-ray absorption spectroscopy is applied to investigate NaAlH4 doped with 5 mol % TiCl3 by ball milling. XANES analysis indicates that after the ball milling Ti species are reduced from Ti (+3) to Ti (0). Release or absorption of hydrogen does not affect the chemical state obtained after ball milling. EXAFS analysis shows that the Ti atoms are associated only with Ti as next neighbors in the ball-milled state as well as during subsequent desorption and absorption of hydrogen. Furthermore, an increase of the particle size and an ordering of the local structure is seen to evolve with the desorption and the absorption of hydrogen.