The catalytic effect of two nanoscale transition metal oxides, Fe2O3 and Co2O3, as additives on the dehydrogenation properties of LiAlH4 after milling are investigated. The onset dehydrogenation temperature for the 5 mol % Fe2O3-doped and 5 mol % Co2O3-doped samples are 85 and 79 °C lower for the first-stage and 60 and 45 °C lower for the second-stage, respectively, compared with the asreceived LiAlH4. The isothermal dehydriding kinetics reveals that the 5 mol % Fe2O3-doped sample can release about 7.1 wt % hydrogen in 70 min at 120 °C, whereas as-received LiAlH4 only releases 0.3 wt % hydrogen under the same conditions. From differential scanning calorimetry (DSC) and Kissinger desorption kinetics analyses, the apparent activation energies (Ea) of the 5 mol % Fe2O3-doped sample are 54.2 and 86.4 kJ/mol for the first two dehydrogenation stages, resulting in decreases of 42.8 and 50% compared with those of as-received LiAlH4, respectively, which are considerably lowered compared with LiAlH4 doped with other reported catalysts calculated by Kissinger method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analyses demonstrate that these finely dispersed Li2Fe2.4O4.6, Fe0.957O, and various Co oxides contribute to kinetics improvement by serving as active sites for nucleation and growth of dehydrogenated products.

Peer Reviewed