X-ray absorption study of Ti-activated sodium aluminum hydride

TL;DR

This study uses X-ray absorption spectroscopy to analyze the oxidation state and local environment of titanium in Ti-activated sodium alanate, revealing surface TiAl3 presence and stable Ti valence during hydrogen cycling.

Contribution

It establishes an empirical relationship between Ti valence and K-edge onset and applies it to determine Ti oxidation states in doped sodium alanate.

Findings

Ti valence is zero in doped sodium alanate.

Ti remains nearly invariant during hydrogen cycling.

Surface Ti exists as amorphous TiAl3.

Abstract

Ti K-edge x-ray absorption near edge spectroscopy (XANES) was used to explore the Ti valence and coordination in Ti-activated sodium alanate. An empirical relationship was established between the Ti valence and the Ti K-edge onset based on a set of standards. This relationship was used to estimate oxidation states of the titanium catalyst in 2 mol% and 4 mol% Ti-doped NaAlH4. These results demonstrate that the formal titanium valence is zero in doped sodium alanate and nearly invariant during hydrogen cycling. A qualitative comparison of the edge fine structure suggests that the Ti is present on the surface in the form of amorphous TiAl3.