NaBH 4 is considered as a promising candidate material for solid-state hydrogen storage due to its high hydrogen content of 10.6 wt %. However, its practical use is hampered by its high thermodynamic stability and slow H-exchange kinetics. In the present work, the effects of Ti-based additives, including Ti, TiH 2, and TiF 3, on the dehydrogenation and rehydrogenation of NaBH 4 (NaH+B) were investigated. It was revealed that all of the titanium-based additives were effective in improving the hydrogen desorption and absorption reactions of NaBH 4, and, among them, TiF 3 possessed the highest catalytic activity. The whole dehydrogenation process for the NaBH 4-0.05TiF 3 sample can be regarded as a two-step process: (i) a preferential reaction (3NaBH 4 + TiF 3 → 3NaF + TiB 2 + B + 6H 2) occurring at around 300 °C, and (ii) the formation of Ti- and F-containing species catalyze the dehydrogenation of the remaining NaBH 4. It was also indicated that the F anion can substitute for anionic H in NaH to form NaF 1-xH x in the case of NaH-B-0.05TiF 3 during the hydrogenation process. Therefore, the observed promotion effect of TiF 3 on the reversible dehydrogenation of NaBH 4 should be understood as arising from the combined effects of active Ti- and F-containing species. Also, FTIR spectroscopy confirmed the presence of amorphous Na 2B 12H 12, in both the dehydrogenated and the rehydrogenated states, which may play a role in the partial dehydrogenation and reversibility observed in NaBH 4 with and without catalyst doping.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films