Evolution, separation and characterization of active species of Ti doped NaAlH_4 for hydrogen storage

摘要

The catalytic mechanism of doped complex hydrides for hydrogen storage remains unconfirmed. Here, we report a simple method to separate the active species of Ti-based catalyst in NaAlH_4 through filtration using tetrahydrofuran (THF) as solvent. XRD patterns and XPS spectra were used to observer the evolution of Ti addition in NaAlH_4+10mol%TiF_3 during ball milling and during hydrogen absorption/desorption cycling. The results show that TiF_3 is reduced to amorphous Ti° gradually during milling, and Al_3Ti intermetallic is formed gradually during cycling. Then active species are separated directly by dissolution and filtration from Ti doped-NaAlH_4 using tetrahydrofuran (THF) as solvent. TEM results show that the average particle size of the obtained Al-Ti nanoparticles is 30-50 nm, and Ti element is uniformly distributed on the Al matrix. The hydrogen desorption experiment indicates the separated Al-Ti nanoparticles exhibit good catalytic effect on NaAlH_4 for hydrogen storage. To the best of our knowledge, this is the first report on separation and characterization of the Al-Ti nanoparticles from Ti-doped NaAlH_4.