DESIGN & PRODUCTS POWER SUPPLIES & BATTERIES
Thin transparent nanogenerator stretches, outputs up to 8W/m2
By Julien Happich Improving on the durability and efficiency of triboelectric
nanogenerators (TENGs) found in literature, researchers from
Nagoya University have devised a transparent and stretchable
TENG that leverages the unique properties of a layer of
carbon nanotubes (CNTs) within a transparent elastomer matrix.
The researchers shared their findings in a paper titled “Highoutput,
transparent, stretchable triboelectric nanogenerator
based on carbon nanotube thin film toward wearable energy
harvesters” published in the Nano Energy journal. The paper
reports several proof-of-concept stretchable TENGs, including
a 12x12cm unit, 92% transparent and able to power 30 blue
LEDs connected in series for each gentle tap from a hand. The
authors also attached a 500μm
thin TENG to the palm of a
nitride glove, connecting it to a string of 16 blue LEDs on the
back of the glove. Gentle claps were enough to instantly power
the LEDs, with a current density as high as 48mA/m2.
Unlike previously reported stretchable TENGs whose output
power remains usually insufficient for practical use, here the
authors report an output power up to 8W/m2 for devices only
requiring a simple fabrication process such as spray coating,
which could easily be scaled up to large areas.
Key to the high TENG efficiency and durability, even under
strain, is the use of a carbon nanotube (CNT) thin film, made of
a randomly oriented single-walled CNT network. The CNTs form
an excellent stretchable conductor with high electrical conductivity,
optical transparency, mechanical durability, and chemical
stability. The stretchable TENG’s output power was also optimized
by modifying the transparent elastomer (PDMS) surface
with a fluorinated plasma.
The glove fitted with a string
of LEDs connected to the
stretchable TENG on the
palm.
Schematic illustration of the
glove with S-TENG and LEDs
wired by stretchable CNT thin
film interconnections.
Schematic of the stretchable
TENG (S-TENG) and
measurement setup.
Photograph of the S-TENG.
The scale bar corresponds to
1cm.
First soft and stretchable thermoelectric module
By RNick Flaherty esearchers in Sweden have developed a soft and
stretchable organic thermoelectric module that can
harvest energy from body heat. The thermoelectric generator
(TEG) developed at the Laboratory of Organic Electronics
at Linköping University uses an organic composite material with
unique properties. It is soft and stretchable with a high electrical
conductivity and good thermoelectric properties.
This makes it ideal for many wearable
applications such as smart clothing, wearable
electronics and electronic skin.
The TEG combines the conducting
polymer PEDOT:PSS for the thermoelectric
properties, a water-soluble polyurethane
rubber for elasticity and an ionic liquid for
softness. This generates a thermoelectric
generator with a high conductivity of over
140 S/cm that can stretch to six times its
length. A test module showed an output
of 212 μV/K, and when the module was connected to varying
load resistors it showed a maximum power output at a load
of 430 Ω, which corresponds to the total resistance of the module.
At this load the maximum power output was 25nW for a
temperature difference of 30 K, which was the theoretical maximum.
The advantage of the new material is that large amounts
can be used to increase the total power output.
PEDOT:PSS is the most common conducting polymer and
is used in many applications, not least due to its good thermoelectric
properties. But thick polymer film is too hard and brittle
to be successfully integrated into wearable electronics. “Our
material is 100 times softer and 100 times more stretchable than
PEDOT:PSS,” said Klas Tybrandt, who leads the group of Soft
Electronics at the Laboratory of Organic Electronics. “The ability
to control the structure of the material both at the nanoscale
and the microscale allows us to combine
the excellent properties of the different
materials in a composite,” he said.
The new composite is also printable.
“The composite was formulated by
water-based solution blending and it can
be printed onto various surfaces. When
the surface flexes or folds, the composite
follows the motion. And the process to
manufacture the composite is cheap and
environmentally friendly,” said researcher
Nara Kim (above).
The researchers see a huge range of new possibilities using
the material to create soft and elastic organic conducting
materials. “There are many ionic liquids, conducting polymers
and traditional elastomers that can be combined to give new
nanocomposites for many applications, such as thermoelectric
generators, supercapacitors, batteries, sensors, and in wearable
and implantable applications that require thick, elastic and
electrically conducting materials,” said fellow researcher Xavier
Crispin.
28 News April 2020 @eeNewsEurope www.eenewseurope.com
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