The effects of titanium precursors on hydriding properties of alanates

An overview is presented of recent advances in the development of new and improved alanates for applications and in the fundamental understanding of how Ti-doping enhances hydrogen absorption. Sample materials were produced using approaches based on direct-synthesis and dry Ti-doping methods. It is desirable to introduce Ti through non-reactive processes to avoid the hydrogen capacity loss that occurs through the formation of inactive byproducts (for example Na-halide from the decomposition of Ti-halides and Na-oxides from the decomposition of Ti-alkoxides). We show, for the first time, that alanates can be Ti-doped using TiH2 or through indirect-doping by pre-reacting TiCl2 with LiH. Both methods result in enhanced kinetics. However, improved rates were achieved only after a prolonged activation period of about a 10 cycles, suggesting that cycling leads to Ti diffusion and substitution into the alanate lattice which provides the mechanism through which Ti-doping enhances kinetics. Thus, the reactive decomposition of Ti-halide and alkoxide precursors in the doping process serves an important but not necessarily required function. Published by Elsevier B.V.