Page 275 - Carbon Nanotube Fibres and Yarns

264 Carbon Nanotube Fibers and Yarns

fiber. The two electrodes were twisted together to form a two-ply yarn
SC. Fig. 10.10E and F show the SEM images of the bare CNT fiber. This
threadlike SC achieved operating voltage up to 1.8 V and energy density as
−3
high as 11.3 Wh cm .
Yu et al. made a stretchable asymmetric SC by firstly wrapping gel electro-
lyte coated CNT@MnO 2 core fiber with a CNT@PPy composite film and
then over-twisting the supercapacitor [94]. The obtained stretchable asymmet-
−2
ric threadlike SC exhibited a specific capacitance of 60.435 mF cm at a scan
−1
rate of 10 mV s and the capacitance performance was well maintained during
−2
repeated stretching to 20% strain. An energy density of 18.88 μWh cm was
achieved for the stretchable SC due to its high specific capacitance and ex-
tended potential window of 1.5 V. Patil et al. proposed a flexible coaxial thread-
like SC constructed by wrapping a PVA/LiClO 4 gel electrolyte-coated Fe 2 O 3 /
CFs core (anode) with a MnO 2 /CNT-web paper (cathode) [95]. The MnO 2 /
CNT-web/PVA-LiClO 4 /Fe 2 O 3 /CFs coaxial SC exhibited a high volumetric
−3
energy density of 0.43 mWh cm with good cycling stability.

10.5 Self-charging supercapacitors
As the most widely available, renewable, and environmentally friendly
resource in the world, the solar energy emitted to the earth is estimated
24
−1
4
to be around 3 × 10 J year , which is 10 times more than the energy
consumption rate of mankind. Photovoltaic electricity generation is the
second-fastest growing source in the world’s power sector. Solar-charged
or photo-SCs include polymer solar cells, dye-sensitized solar cells
(DSSCs), quantum dot solar cells, and the recently developed perovskite
solar cells. In a DSSC-based photo-SC, the DSSC serves as the elec-
tron contributor in the presence of light when dye molecules are struck
by photons. The irradiated electrons are transferred from the DSSC via
external circuit and stored in the reservoir of an SC. The charge and
discharge process for the photo-SC mimic the working principles of an
individual SC. The utilization of solar energy to initiate the generation
of photoelectrons instead of electrical energy by a power source is the
only distinctive feature differentiating the photo-SC concept from an
ordinary SC.
Chen et al. [96] reported a high performance threadlike “integrated
energy wire” consisting of a DSSC and an SC. Titania nanotubes radially
grown on a titanium wire were used as the core electrode for both the so-
lar cell and the SC while a CNT fiber was wrapped around the titanium