Biomedical Engineering Reference
In-Depth Information
carbon coating applications on SnS
2
for lithium ion batteries applications. Similar conclu-
sions were also given by EIS plots.
Supercapacitance
Supercapacitors are highly attractive energy storage devices for their exceptionally high-
power and energy-density characteristics compared with conventional dielectric capaci-
tors and to their long cycle life in the applications of batteries. Certain kinds of metal
oxide, such as RuO
2
, MnO
2
, and NiO
2
, have already been applied as a contribution for
carbon-based supercapacitors [165,191]. Recently, graphene material has been considered
for high mobility, chemical, and mechanical stability due to its unique structure of two-
dimensional layer hexagonal lattice of carbon atoms [192]. Kalpana et al. [193] fabricated
ZnO/carbon aerogel composite electrode with a specific high capacitance of 500 F/g. In
2009, Zhang and Pan [194] investigated graphene-ZnO composite film as an electrode for
supercapacitor. The graphene was pasted on the indium tin oxide glass substrate. The
graphene was fabricated by a modified Hummers method, and then ZnO was deposited
by ultrasonic spray pyrolysis at a frequency of 1.65 MHz. The as-made graphene, pure
ZnO film, and graphene-ZnO composite films were named ITO-G, ITO-ZnO, and ITO-
G-ZnO, respectively, for EIS study. 1 M KCl solution was used as electrolyte, and the fre-
quency range is from 10 kHZ to 10 MHz. Figure 4.37 shows the Nyquist plots of different
electrodes.
In Figure 4.37, the high-frequency arc is ascribed to the double-layer capacitance (
C
dl
)
in parallel with the charge transfer resistance (
R
ct
) at the contact interface between the
electrode and the electrolyte solution. In the low frequency, the result is explained by
the electrode surface inhomogeneity and the existence of CPE. The resistance
R
ct
values,
which is calculated from the diameter of the high-frequency arc, are 17 and 3
Ω
for ITO-G
and ITO-G-ZnO, respectively. The electrochemical measurement shows that graphene-
ZnO composite film enhances the capacitive properties more than pure graphene or ZnO
electrode.
Guo et al. [195] used graphene nanosheets (GNSs) as anode material for lithium-ion
batteries. The GNSs were prepared using artificial graphite (AG) as material by a rapid
(a)
(b)
1000
75
800
ITO-ZnO
60
ITO-G-ZnO
600
45
400
30
200
15
ITO-G
0
0
100
120
140
160
180
15
30
45
60
75
90
Z'
(Ohm)
Z'
(Ohm)
FIGURE 4.37
Nyquist plots for ITO-G-ZnO, ITO-G (a), and ITO-ZnO (b). (From Zhang, Y.,
J. Electroanal. Chem.
Interfacial
Electrochem.
, 634, 68, 2009. With permission.) [194]
