Significantly Improved Dehydrogenation of LiAlH4 Destabilized by MnFe2O4 Nanoparticles

The effects of nanosized MnFe2O4 additive on the dehydrogenation properties of LiAlH4 prepared by ball milling were investigated for the first time. It was found that the LiAlH4 + 7 mol % MnFe2O4 sample started to decompose at 62 and 119 °C for the first two dehydrogenation stages and released 7.45 wt % hydrogen, which is 88 and 71 °C lower than those of as-received LiAlH4, respectively. The isothermal dehydriding kinetics show that the doped LiAlH4 sample could release about 4.7 wt % hydrogen in 70 min at 90 °C. Furthermore, the first two dehydrogenation steps could be finished within 80 min with 7.44 wt % hydrogen released at 120 °C, whereas as-received LiAlH4 only released about 0.5 wt % hydrogen for the same temperature and time. From differential scanning calorimetry (DSC) and Kissinger desorption kinetics analyses, the apparent activation energies, Ea, of the doped sample were 66.7 kJ/mol for the first dehydrogenation stage and 75.8 kJ/mol for the second dehydrogenation stage, resulting in decreases of 40.2% and 58.1% compared with those of as-received LiAlH4, which are much higher than those of LiAlH4 doped with other reported catalysts calculated by Kissinger method. Through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) observations, in situ formed Fe0.9536O and amorphous Mn or Mn-containing phases together provide a synergetic catalytic effect for the remarkably improved dehydrogenation properties of LiAlH4.