Material 2
Material 1
Electrode
Electrode
Initial state Press Release
Materials charge up
42
DISCOVERMAGAZINE.COMC
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Triboelectricity’s glow eventually
faded. In 1831, British physicist Michael
Faraday unveiled the first electromagnetic
generator, which uses a moving magnet
to induce an electric current in a coiled
wire. That changed everything. Today, the
generators in coal plants, wind turbines,
nuclear power plants and hydroelectric
dams — basically anything that works
by converting physical movement into
electricity — has an electromagnetic
generator at its heart.
Only photocopiers still make use of
static electricity, in the form of distributed
charges to direct ink on paper. For the
most part, it’s been punted to the status of
an everyday nuisance that falls somewhere
between mildly annoying and extremely
dangerous. We go down plastic slides and
get shocked on the dismount; we’re told
not to use cellphones or sit in cars when
pumping gas because stray charges can
spark fumes. Lightning, the most violent
display of static electricity, kills dozens of
people every year in the U.S.
Until 2010, Wang barely gave a second
thought to static electricity. He never
meant to spark an energy revolution.
But what he calls a happy accident in the
lab revealed that triboelectric materials
could produce big voltages,
setting the scientist on a path
to harvest them.
SHOCKING BEGINNINGS
Early in his career, Wang was
motivated by the allure of dis-
covering new materials and
new phenomena, “regardless of
if they had an application,” he
says. But that outlook changed
in the late 1980s, when he
started working at Oak Ridge
National Laboratory in
Tennessee and saw scientists
using new materials to solve
real-world problems. By the
time he moved to Georgia Tech in 1995,
where he’s been ever since, his work had
a clear purpose. “I only wanted to study
materials that really had a benefit,” he says.
His new projects always begin with the
same question: What can we use this for?
In 2005, Wang focused his lab on
designing devices that could power them-
selves. He worked with piezoelectric crys-
tals, which generate sparks when they’re
bent, compressed or otherwise deformed.
They were first identified by Marie Curie’s
husband more than 100 years ago, but
the materials tend to be brittle and hard
to work with.
Eight years ago, Wang and his graduate
students were testing a
device, a sort of electric
sandwich made of thin
slices of piezoelectric
materials. The engineers
were having trouble
removing all the air gaps
between the layers, which
they assumed would ham-
per the electric flow of the
device. When they tested
the design, however,
they recorded a higher
voltage — three to five
times higher — than they
expected.
“We thought it had to
be an artifact of the testing,” Wang says,
referring to experimental error.
It turned out some air gaps remained,
which meant that something other than
the piezoelectric effect was responsible.
The team realized the voltage must result
from charges exchanged when the mate-
rials rubbed together: static electricity.
That realization was a defining event in
Wa n g ’s r e s e a r c h.
IT DOESN’T TAKE MUCH
By 2012, Wang’s group had developed the
first triboelectric nanogenerator (TENG).
Despite the diminutive-sounding name,
the generators range in size from a few
The team realized
the voltage
must result
from charges
exchanged when
the materials
rubbed together:
static electricity.
Rubbing together
differently charged
materials, like a
glass rod on silk,
creates static
electricity.
Objects further
apart on this
sample list of
materials will
generate a
stronger charge.
TENGs, or triboelectric
nanogenerators,
harness the small
sparks of static
electricity. When
two materials press
together, they
exchange charges,
which connected
electrodes can turn
into an electric
current. At left, a
researcher uses a
TENG to power this
scientific calculator.
Materials and polarity
More
Positive
(tend to lose
electrons)
More
Negative
(tend to gain
electrons)
Neutral
Hair
Nylon
Glass
Fur
Silk
Aluminum
Paper
Cotton
Wood
Wool
Steel
Acrylic
Amber
Rubber
Polyester
Styrene
Silicon
Vinyl (PVC)
Teflon