Enhanced hydrogen storage properties of LiAlH4 catalyzed by CoFe2O4 nanoparticles

Abstract

The catalytic effects of CoFe₂O₄ nanoparticles on the hydrogen storage properties of LiAlH₄ prepared by ball milling were investigated. The onset desorption temperature of the LiAlH₄ + 2 mol% CoFe₂O₄ sample is 65 °C, which is 90 °C lower that of the as-received LiAlH₄, with approximately 7.2 wt% hydrogen released at 250 °C. The isothermal desorption results show that for the 2 mol% CoFe₂O₄ doped sample dehydrogenated at 120 °C, 6.8 wt% of hydrogen can be released within 160 min, which is 6.1 wt% higher than that of the as-received LiAlH₄ under the same conditions. Through the differential scanning calorimetry (DSC) and the Kissinger desorption kinetics analyses, the apparent activation energy, E_a, of the 2 mol% CoFe₂O₄ doped sample is calculated as 52.4 kJ mol⁻¹ H₂ and 86.5 kJ mol⁻¹ H₂ for the first two decomposition processes. This is 42.4 kJ mol⁻¹ H₂ and 86.1 kJ mol⁻¹ H₂ lower compared with the pristine LiAlH₄, respectively, indicating considerably improved dehydrogenation kinetics by doping the CoFe₂O₄ catalyst in the LiAlH₄ matrix. From the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses, a series of finely dispersed Fe and Co species with a range of valence states, produced from the reactions between LiAlH₄ and CoFe₂O₄, play a synergistic role in remarkably improving LiAlH₄ dehydrogenation properties. The rehydrogenation properties of the LiAlH₄ + 2 mol% CoFe₂O₄ sample have also been investigated at 140 °C under 6.5 MPa pressure held for 2.5 h.