Biomedical Engineering Reference
In-Depth Information
has demonstrated to be a suitable material to
provide high performances.
In order to enhance the charge storage, supercapacitor devices
propose the use of high surface electrodes. Two main inorganic
materials have been successfully essayed. In activated carbons,
an electrochemical double-layer is formed at the electrode-
electrolyte interfacial regions. However, the low capacitance values
(10-40 F cm
In both devices, TiO
2
) exhibited are an important drawback for their extended
use of nonfaradaic supercapacitors. Nanostructured metal oxides
supercapacitors are based on a pseudocapacitive effect involving
a dependency between voltage and a faradaic reaction. It has been
demonstrated that higher energy densities can be achieved without
significantly penalizing power rate and long life cycling of double
layer capacitors. These asymmetric supercapacitors are assembled
with a high surface carbon and the metal oxides using an aqueous
solution as electrolyte. The faradaic reaction here involved is
expected to provide charge devices to fill the gap between capacitors
and batteries. Hydrous ruthenium oxide provides high capacitance
values (720 F g
-
2
) but is very expensive. Hence, less alternative less
costly materials were searched including manganese oxide, iron
oxide, vanadium oxide, etc. [53].
TiO
-
1
is a not electronically
conductive material which is usually used in the dielectrically
capacitors but should not be suitable for supercapacitors based
on pseudocapacitive effects. In turn, titania has demonstrated
to be an excellent matrix to favor the dispersion of other active
materials. Moreover, an ordered multiporous morphology should
provide more real surface areas for the faradaic reaction through an
accessible interface for mass and charge transfer reactions. Dunn et
al. have reported that the pseudocapacitive contribution to charge
storage in anatase TiO
2
is a low cost material, however, TiO
2
2
nanocrystals is significantly enhanced
for particle sizes lower than 10 nm. Thus, total stored charge and
charge/discharge kinetics were improved [54]. Thus, several
examples have been reported including RuO
2
on TiO
2
nanotubes
[55] Co(OH)
2
on TiO
2
nanotubes [56]. However, the powdered TiO
2
nanotubes are usually disorderly arranged and features very small
tube size (<10 nm) hindering the entering of the transition metal
particle into the inner surfaces of nanotubes during the compositing
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