Significantly improved dehydrogenation of LiAlH 4 catalysed with TiO 2 nanopowder

Abstract

The effects of TiO 2 nanopowder addition on the dehydrogenation behaviour of LiAlH 4 have been studied. The 5 wt.% TiO 2-added LiAlH 4 sample showed a significant improvement in dehydrogenation rate compared to that of undoped LiAlH 4, with the dehydrogenation temperature reduced from 150 °C to 60 °C. Kinetic desorption results show that the added LiAlH 4 released about 5.2 wt% hydrogen within 30 min at 100 °C, while the as-received LiAlH 4 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 LiAlH 4 and 49 kJ/mol for the 5 wt.% TiO 2 added LiAlH 4, indicating that TiO 2 nanopowder adding significantly decreased the activation energy for hydrogen desorption of LiAlH 4. 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 LiAlH 4 due to admixture of TiO 2 after milling. X-ray photoelectron spectroscopy results show no changes in the Ti 2p spectra for TiO 2 after milling and after dehydrogenation. The improved dehydrogenation behaviour of LiAlH 4 in the presence of TiO 2 is believed to be due to the high defect density introduced at the surfaces of the TiO 2 particles during the milling process.