J.-H. Shim et al. / Journal of Alloys and Compounds 417 (2006) 69–71
71
tion. It is noted that Li3AlH6 catalyzed with TiAl3 releases
larger amount of hydrogen (4.5 wt.%) than TiCl3 (4.0 wt.%) as
expected. This is because TiCl3 decomposes part of Li3AlH6
during milling for dispersion before dehydrogenation and thus
decreases the hydrogen storage capacity of Li3AlH6. Therefore,
it will be favorable to add TiAl3 instead of TiCl3 into alanates
in order to minimize the loss in hydrogen storage capacity.
4. Conclusions
Ultrafine TiAl3 powder has been synthesized using a
mechanochemical reaction between TiCl3, AlCl3 and Mg. The
primary particle size of TiAl3 is around 100 nm and its particle
shape is irregular. The addition of ultrafine TiAl3 decreases the
dehydrogenation temperature of Li3AlH6 by about 30 ◦C com-
pared to Li3AlH6 without any catalyst. Although TiCl3 is more
effectiveinreducingthehydrogenationtemperature, itisdemon-
strated that the use of ultrafine TiAl3 catalyst is more favorable
than TiCl3 in terms of hydrogen storage capacity.
Fig. 4. DSC curves of Li3AlH6 with and without catalysts.
Without catalysts, Li3AlH6 start to decompose releasing H2
gas (dehydrogenation) at about 190 ◦C and the peak tempera-
ture is about 210 ◦C. On the other hand, the dehydrogenation of
Li3AlH6 containing TiAl3 start at about 160 ◦C and exhibit the
peak at about 180 ◦C. This decrease in dehydrogenation temper-
ature is quite large compared to those of Balema et al. [2] and
Resan et al. [10]. This might be attributed to the ultrafine particle
sizeofTiAl3 preparedinthepresentwork. However, thecatalytic
effect of ultrafine TiAl3 is not comparable to that of TiCl3 show-
ing the dehydrogenation starting temperature of about 130 ◦C.
It is not fully understood yet why there exists a difference in
catalytic ability between TiAl3 and TiCl3. This is presumably
because the in situ formation and dispersion of TiAl3 by the
reaction between TiCl3 and Li3AlH6 is more advantageous than
the direct dispersion of TiAl3 in aspects of the uniform disper-
sion and fine particle size of the catalyst and oxide layers on
the surface of the TiAl3 particles formed during the preparation
decrease the catalytic ability.
Acknowledgements
This work has been financially supported by the Hydrogen
Energy R&D Center under the 21st Century Frontier R&D Pro-
gram of the Ministry of Science and Technology, Republic of
Korea.
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