Significantly improved dehydrogenation of LiAlH4 catalysed with TiO2 nanopowder
The effects of TiO2 nanopowder addition on the dehydrogenation behaviour of LiAlH4 have been studied. The 5 wt.% TiO2-added LiAlH4 sample showed a significant improvement in dehydrogenation rate compared to that of undoped LiAlH4, with the dehydrogenation temperature reduced from 150 °C to 60 °C. Kinetic desorption results show that the added LiAlH4 released about 5.2 wt% hydrogen within 30 min at 100 °C, while the as-received LiAlH4 just released below 0.2 wt.% hydrogen within same time at 120 °C. From the Arrhenius plot of the hydrogen desorption kinetics, the apparent activation energy is 114 kJ/mol for pure LiAlH4 and 49 kJ/mol for the 5 wt.% TiO2 added LiAlH4, indicating that TiO2 nanopowder adding significantly decreased the activation energy for hydrogen desorption of LiAlH4. X-ray diffraction and Fourier transform infrared analysis show that there is no phase change in the cell volume or on the Al–H bonds of the LiAlH4 due to admixture of TiO2 after milling. X-ray photoelectron spectroscopy results show no changes in the Ti 2p spectra for TiO2 after milling and after dehydrogenation. The improved dehydrogenation behaviour of LiAlH4 in the presence of TiO2 is believed to be due to the high defect density introduced at the surfaces of the TiO2 particles during the milling process.