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, E
a, 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.
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