Sponsored by Cometeer.
100 times stronger than steel are fascinating materials that could *channel* a kaleidoscope
of futuristic technologies. They’re often hailed as a key *conduit* for a speedy transition
to a zero-carbon energy future. However, while these graphene-based tiny tubes have been
overhyped as revolutionary for about 30 years, they haven't made it to the market yet. But
we're seeing slow progress towards interesting use cases, like a recent advancement that
could turn CNTs into *hot stuff* for generating clean electricity out of waste heat. Let's
revisit carbon nanotubes and see how things are shaping up.
I'm Matt Ferrell ... welcome to Undecided.
About a year ago I covered how carbon nanotubes might be able to boost solar energy in another
video, so I thought it was a good time to revisit the topic. And I'm not a scientist,
but like to look at these technologies from a broader view, how they may impact our lives,
and if they're actually coming to market. I know you've probably heard a lot of promises
on graphene and carbon nanotubes that haven't been delivered yet, but researchers are unleashing
new avenues to *channel* their phenomenal potential, as well as finding ways to improve
their manufacturing. And it's that last point that's one of the biggest sticking points
with CNTs.
Let's refresh your memory *and mine as well* on what’s meant to be the *hollow grail*
of the nanotechnology field. Although CNTs were first observed
in the late 1950s , formed by two layers of graphene. Not exactly catchy names, but very
accurate.
Since Iijima brought them to life, CNTs have been associated with endless fanciful applications.
Like a space elevator to name the most *out there* prediction. However, the *astronomical*
promise has never been fulfilled. One reason for this is that when you try to spin CNTs
into long fibers, their exceptional strength shrinks by 100 times. Now, I’m obviously
dubious whether CNTs will ever elevate us into space, but they can certainly conduct
electricity. That's because each carbon atom has a spare electron which can’t wait to
flow around. While MWCNTs conductivity isn't affected by the material geometry , SWCNTs
can have a metallic or semiconducting behavior based on the way the graphene layer is twisted,
a.k.a. the chiral angle. As a result, you can end up with a more or less conductive
configuration by design, like armchair, zig-zag, and chiral nanotubes. Again, you've got to
love the names ... armchair? Anyway, CNTs with an armchair structure are similar to
metals from the electric point of view. That’s why they’re the focus for making power cables.
But the challenge is being able to make these nanowires as long as possible.
Back in 2014, after years of lab work, researchers at Rice University *knitted* nanotubes into
a fiber that carried 4 times more current than copper. When filling a cable, these armchair
DWCNT wires can transfer power over longer distances while sustaining lower losses compared
to copper. You may see why their scale-up could make our grid so much more efficient.
But we have a *macro* problem. It’s very difficult to mass produce pure armchair CNTs,
which I'll get to in a minute.
Other than potentially improving grids, researchers have recently opened up a new *thread* for
CNTs: Making the most out of waste heat. Just think of sources like solar panels or power
plants.
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Now back to the hot carbon nanotube advancement...
According to the US Energy Information Agency, over 60% of the energy used for generating
electricity in America is lost as heat. Well, apparently CNTs may be a good fit for recovering
this unused thermal power and upcycling it into renewable electricity. And there seems
to be a *common thread* in the innovators here. Once again, Rice University. After improving
power cables, Rice scientists used SWCNTs ... wait, rice scientists? I think that's
a completely different thing ... Rice University scientists used SWCNTs to make a waste heat-to-energy
device. Basically, they designed a carbon nanotubes film containing cavities that trap
the infrared heat from the sun and narrow its bandwidth. When doing so, they give off
photons, which can be efficiently converted into electricity. Researchers claim that integrating
their heat-recovery device within solar panels would boost their efficiency up to 80%. Compared
to solar panels available on the market today, which don't go above about 23%, that sounds
dramatic. But you'd need to compare those to the efficiencies in other lab solar cell
tests, which are around the 50% mark. So this claim still needs to be vetted and work its
way out of the lab.
Just this August Rice University researchers revamped their tailoring skills and released
their latest tubular collection ... a CNT-containing textile that turns heat into electricity.
This could set a new fashion trend in the green energy world. Donning their dressmaker’s
hats, scientists have used a sewing machine to craft a smart cloth out of DWCNTs fibers.
As it turns out, this tubular dress is a thermoelectric generator. Basically, it can convert sunlight
and other heat sources into electricity. During a lab experiment, jointly set up by Tokyo
Metropolitan University and Rice University Carbon Hub, this *supercharged* fabric used
the heat from a hotplate to turn on an LED light . It may not sound like a *powerful*
achievement to you, but this new CNT clothing line hit a record-breaking power factor which
is three times larger than the commercial standard.
But how does that work? Essentially, you generate electricity whenever there's a temperature
gradient across the material. Meaning that one side of it is hotter than the other. Funny
as it sounds, individual nanotubes hold a *giant* power factor. This is the energy density
you can get out of a material depending on a particular temperature difference. There
are two components affecting the power factor of a material. Its electrical conductivity
and the so-called Seebeck coefficient , a.k.a. thermopower, which gives you an indication
of how much electricity a material generates out of thermal variations. Imagine you join
two wires made of different metals and you heat up one of them. When you do that, electrons
will flow towards the cooler part of this circuit. Well, Seebeck was the first one to
*see* that, which is why this phenomenon is called the Seebeck effect. And it’s the
basic principle of how thermocouples work. So far, scientists have struggled to preserve
the CNTs power factor when weaving them together into a larger framework like a fabric ... until
now. The Rice group ... sorry, the Rice University group was the first at creating a large-size
CNTs-based structure that retains the superior energy density of the individual tubes.
They managed to pack the fibers into a dense and highly aligned pattern. This led to an
electrical conductivity over 10 times higher than those measured in the past for CNT macrostructures.
On top of that, designers played around with the CNTs’ Fermi energy. This can be defined
as the difference between the highest and the lowest kinetic energy level of electrons
at 0 kelvin (ca. -460 F). At any other temperature, you refer to the Fermi level instead, which
is often called electrochemical potential. Now, I'm not a scientist, so if I missed anything
here, sound off in the comments. I know it all sounds complicated so let’s focus on
a keyword: kinetic. Adjusting the Fermi energy, or level, will affect how fast electrons move
throughout the material. In other words, the electric conductivity. A successful tuning
of this parameter allowed researchers to tweak the fibers' electronic properties. They doped
the textile with some chlorine-containing chemicals and achieved a higher Seebeck coefficient,
which means having a more efficient nanocouple.
Obtaining a very high power factor is crucial for energy harvesting applications because
you maximize the electricity output you get when tapping into renewable sources like solar
or industrial waste heat. For the sake of the experiment, scientists tested centimeters-long
fibers. However, researchers obtained the same electronic properties after plying the
smaller fabric pieces into longer CNTs threads, which means the product is scalable.
The major caveat here is that it's only been proved in the lab, but it's a very encouraging
result as energy-efficient CNT macrostructures will be essential to develop real-world energy
harvesting devices. And that’s what the research group is planning to develop further
in the future. A possible application would be active cooling of electronics. Thanks to
their high thermal conductivity, the nanotube fibers could draw heat out of sensitive optoelectronics
that may otherwise fail when exposed to high temperatures. While they haven’t disclosed
any funding from private investors, this research was supported by a few foundations as well
as by the US Air Force and Department of Defense.
Although these recent developments are *heating up* the vibes around CNTs, it’s taking ages
to commercialize these revolutionary materials. So, what’s been obstructing the tube between
the lab and the market?
The main challenge has been developing larger CNT-based structures that preserve the marvelous
properties of each of their building blocks. Another major conundrum has been selectively
growing a nanotube with a specific geometry. Whenever creating CNTs, you always end up
having a *cocktail of nano-straws* with different shapes and properties. And, most importantly,
this clumping mess doesn’t have the wondrous qualities of single CNTs. However, over the
last year or two researchers have come up with different methods to disentangle the
CNTs clustering issue.
One of scientists’ main goals has been to separate metallic and semiconducting tubes.
To achieve this, they developed different kinds of polymers to dissolve and wash away
one type while leaving the other one behind. Another team of researchers used cresol, an
ingredient of commercial cleaning products, to purify the CNTs jumble. In addition to
avoiding harsh chemicals that could reduce CNTs conductivity, using cresol gave the isolated
tubes a sticky twist. As researchers increased the amount of cresol, their purified product
changed consistency from toothpaste-like to gel to a sort of charcoal dough that basically
behaves like plastic. This is still in the lab phase, so more testing and development
is happening, but their polymer-like creation could bring massive practical advantages.
It'd be much easier to handle and carry around compared to fluffy carbon powders. And they'd
be more suitable for composite industrial production.
After 30 years, CNTs pioneer Sumio Iijima hasn’t lost his early enthusiasm and is
still trying to accelerate carbon nanotubes mass production. Apparently, he filed a patent
for a new method that would tidy up the CNT mess you normally get. All these contributions
could make life easier for the few companies who are working hard to commercialize them.
Like Huntsman Corp, which has been able to increase production from a gram an hour to
being able to create a kilogram an hour. That's a 1000 times increase in a few years and they're
continuing to scale it up.
The hype on carbon nanotubes isn't as high today as it was 30 years ago, which is a good
thing. I think the expectations are more realistic now. But they’re still some of the most
promising materials for the future of green technologies. While manufacturing CNTs at
scale has worked out to be far more complex and time-consuming than expected, researchers
have made significant, albeit slow, progress. Clearly, they still can’t promise us a space
elevator, but harvesting heat for energy and making our grid and solar panels more efficient
sounds like an electrifying, yet down-to-Earth, achievement. It's important to keep our eye
on the progress ... and expectations in check.
But what do you think? Do you think this type of tech is going to make a difference in the
renewable market? Or do you think CNTs have still been overpromised and will never deliver?
Jump into the comments and let me know. And thanks as always to my patrons. Their direct
support really helps with producing these videos. Speaking of which, if you liked this
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