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In the low-frequency region, each Nyquist plot exhibited a
straight line, Warburg portion, toward the Z0 real axis with
an increase in the imaginary part (–Z00-axis). As can be seen
from Figure 11(a), the Warburg regions of Device I and
Device II are longer than that of Device III. This difference
between impedance characteristics is thought to be a result
of relatively slower ion diffusion rates and longer diffusion
pathways in the polymeric networks of PTTOBu and PTTO-
Hex. The more suitable 3D-dimensional morphology of
PTTOOct conducting film helped to improve ion movements
in Device III by offering sufficient and shorter diffusion path
lengths compared with the morphologies of PTTOBu (Device
I) and PTTOHex (Device II). Moreover, the Warburg region of
Device III has also a steeper slope than those of Device I and
Device II. This means that an electrochemical double-layer
was formed faster on PTTOOct surface and it had a better
capacitive performance under the same condition. In addi-
tion to Nyquist plots, the Bode-phase angle plots were also
recorded in the frequency range of 104 to 1022 Hz [Fig.
11(b)]. In the Bode plots, the phase angles of Device I,
Device II, and Device III corresponded to 273.88, 277.28,
and 280.48 at 1022 Hz. According to Bode-phase angle anal-
yses, it can be said that Device III has a better pseudocapaci-
tive performance than Device I and Device II since the
capacitive behavior in the low-frequency region is usually
determined with the phase angle approaching 2908. These
experimental data also prove that PTTOBu, PTTOHex, and
PTTOOct exhibit good electrochemical capacitive properties
and claim potential application as redox-active electrode
materials in energy storage devices.
retentions upon long-term charge/discharge cycling after
10,000 cycles. In this context, the capacitive performances of
PTTOBu, PTTOHex, and PTTOOct were found to be compara-
ble to various polymeric redox electrode materials such as
PTh,
PPy,
and
PANI
derivatives,
previously
reported.17,39–45,47,52–57 The results reveal that molecular
design strategy could be beneficial for the preparation of
novel psuedocapacitive electrode materials with controllable
morphology and improved performance.
ACKNOWLEDGMENTS
The authors thank the Scientific and Technological Research
€ _
Council of Turkey (TUBITAK, Grant No: KBAG-114Z167) for
ꢀ
financial support. D. Yigit is also generously supported by
€ _
TUBITAK KBAG-114Z167 with a postdoctoral scholarship.
€
They also would like to thank Elif Akhuseyin Yıldız for her
assistance with the SEM observations.
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In summary, we successfully prepared a series of the novel
poly(terthiophene) derivatives, PTTOBu, PTTOHex, and
PTTOOct, specifically designed to control the morphology of
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PTTOOct redox-active electrode material delivered higher
maximum specific capacitance (443 F g21) than PTTOHex
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which allows easier and faster ion diffusion. In addition,
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