## GWU team demonstrates highly scalable, low-cost process for making carbon nanotube wools directly from CO2

##### 19 July 2017

Researchers at George Washington University led by Dr. Stuart Licht have demonstrated the first facile high-yield, low-energy synthesis of macroscopic length carbon nanotubes (CNTs)—carbon nanotube wool—from CO2 using molten carbonate electrolysis (earlier post).

The resulting CNT wool is of length suitable for weaving into carbon composites and textiles and is highly conductive; the calculated cost to produce the CNTs is approximately $660 per ton, compared to the current$100,000+ per ton price range of CNTs. A paper on the work is published in the journal Materials Today Energy.

The CNT wool process builds on earlier work by Professor Licht and his team to develop a one-pot process that transforms CO2 into a controlled selection of nanotubes (CNTs) via molten electrolysis: C2CNT (CO2 into carbon nanotubes). This synthesis consumes only CO2 and electricity, and is constrained only by the cost of electricity. The initial synthesis pathways, however, led only to short CNTs.

Whereas our previous molten carbonate synthesized CNTs have nanometer-sized diameter and lengths, this CNT wool reaches diameters over 1 mm and length over 1 mm. Hence, the question arises whether this new CNT wool should be classified as a nanomaterial. The physical properties, such as the unusually high electrical conductivity and Raman spectra of these materials demonstrated in the linked Data in Brief paper are that of multi-walled carbon nanotubes, and are due to the morphology as demonstrated by TEM.

The length to diameter ratio and the 0.342 nm inter-wall spacing of these confined cylindrical graphene layers suggests these new CNT wools should be classified as a (albeit unusual, but particularly useful as a cloth precursor, class of) CNT material. Monel cathode substrates, electrolyte equilibration, and a mixed metal (NiChrome) nucleation facilitate the synthesis of this CNT wool. The process is constrained by the (low) cost of electricity. Carbon dioxide is the sole reactant in this CNT transformation, providing a financial impetus for the removal of this greenhouse gas.

—Johnson et al.

 Schematic representation of new synergistic pathways to form a high yield of macroscopic length CNT “wool” by electrolysis in molten carbonate. Left side: experimental cell configuration used in these C2CNT experiments. Middle: Prior C2CNT syntheses were dependent on a zinc coated steel cathode, a pure Ni anode, and a low current pre-electrolysis activation step. An intermediate, new C2CNT electrolysis removes the requirement of a zinc coating leading to the exploration of a variety of new cathode substrates. Right side: The optimized C2CNT pathway utilizes Monel cathodes and Nichrome anodes, molten electrolyte equilibration for 24 h, and the electrolysis is conducted directly without pre-electrolysis activation steps. This pathway produces a high yield of macroscopic length CNT wool. Johnson et al. Click to enlarge.

The new process grows the CNTs on Monel (nickel alloy) instead of steel. Monel, electrolyte equilibration, and a mixed metal nucleation facilitate the synthesis.

Efficacious climate mitigation by CO2 transformation requires a massive market, and product stability and compactness. The most compact form of captured carbon is through its transformation to solid carbon. CNTs are among the highest strength and most stable materials. CNT cost reduction by C2CNT, provides a preferred (lower mass per unit strength) to the mass metal market, and the CNT wool introduced here accelerates CNT demand as a building industry and textile material. Together these principal societal staples, when produced from CO2, comprise an ample demand to markedly decrease atmospheric carbon.

… Initial scaling is efficiently applied to available concentrated, hot sources of CO2, such as eliminating the CO2 emission from industrial smoke stacks and simultaneously forming valuable CNT wool. Larger scale C2CNT can be achieved through direct elimination of atmospheric CO2 using solar heat and solar to electric PVs.

—Johnson et al.

The team calculated that an area equal to only 4% of the Sahara Desert would be sufficient to bring atmospheric CO2 concentrations back to pre-industrial levels in ten years, and that a wind speed of 1 km per hour would be sufficient to deliver that CO2 to those STEP (solar thermal electrochemical process (STEP) CNT plants (earlier post).

 Schematic representation of an ocean-based solar thermal and photovoltaic field to drive both water purification and C2CNT splitting of CO2 to useful products. Johnson et al. Click to enlarge.

Resources

• Marcus Johnson, Jiawen Ren, Matthew Lefler, Gad Licht, Juan Vicini, Xinye Liu, Stuart Licht (2017) “Carbon nanotube wools made directly from CO2 by molten electrolysis: Value driven pathways to carbon dioxide greenhouse gas mitigation,” Materials Today Energy, Volume 5, Pages 230-236 doi: 10.1016/j.mtener.2017.07.003

Can't wait they use this process to remove the excess co2 in worldwide atmosphere and it won't cost anything if they can sell these products to the industry. The climate change treat is over everybody. Now stop subsidizing evs, hydrogen and solar and windmills. I can also now buy my gas for my car without any carbon taxes associated with it.

I don't know if this article will bring many comments but i say this is the best way to resolve climate change and save trillions of dollars.

Interesting fact from the history of Petroleum - Gasoline was around before the invention of the internal combustion engine but for many years was considered a useless byproduct of the refining of crude oil to make kerosene.
So todays useless CO2 waste product may be more valuable than just burning Natural Gas. The future of the Fossil Fuel Industry may be the production of CNT and Carbon Fiber from CO2. Net Power (netpower.com) has a technology which uses a supercritical CO2 cycle that makes carbon capture part of the core power generation process. This could be combined with the GWU process to close the loop creating Carbon Capture and Reuse.

Another Carbon Reuse project could use Natural Gas Pyrolysis like the Monolith Carbon Black Plant (see http://spectrum.ieee.org/energywise/energy/fossil-fuels/nuclear-to-coal-to-hydrogen-sheldon-station-blazes-a-trail). This process uses "waste" Hydrogen to run the electric plant. Again the valuable product is Carbon Black for CNT.

Saudi-arabia, mexico and u.s.a should use this process to protect the fossil fuel industry from the paris climate agreement and stop this recession provoked by massive bleeding of tax money given to green technologies for nothing finally.

You still have to capture the carbon and then invest the energy to reduce it.  Given that the ΔHf of CO2 is -393.52 kJ/mol, reducing 1 ton of CO2 to fixed carbon will take a whopping 2.48 megawatt-hours plus losses.

On the other hand, if this process is reversible (converting fixed carbon back to CO2 and electricity) it could be the basis of a carbon-based storage battery.

The sooner we can get away from digging the stuff out of the ground the better. Plenty already in circulation for our needs. Nice to see renewable energy is making this possible.

Now we still have the other toxins from fossil fuels to be concerned about. NOx, SOx, mercury, arsenic and on and on.

Assuming per ton energy requirement with losses is 5MWH and energy price is $50/MWH, Energy cost/ton is$250, about a third of the calculated CNT cost cited in the article, which is in the ballpark of the cost of steel.
Solar/Wind auctions are down to $20/$40 MWH in places; it's not unreasonable to expect energy cost to continue falling. If this stuff could be used for building material, that would be something.

It could certainly be used to make FRP composites, maybe even conductive ones.  If the yarns spun from it are conductive, it could be used to make ultra-lightweight wire for power transmission.  Weaving together insulated conductors would make it immune to skin effect.

If you're buying electricity at $20/MWh, your cost of CO2 removal is a minimum of$49/ton (and probably more like $100/ton). If CO2 emissions are priced at$100/ton, it adds about 3.3¢/kWh to the cost of power from a CCGT plant and about 5¢/kWh to power from an OCGT plant burning natural gas.

At that point, nuclear power becomes a no-brainer.  You build it out to serve the full base load plus some extra to keep your CO2-reduction systems hot.  If RE is much cheaper than nuclear, you can dump excesses to the CO2 reduction systems and convert the energy to fixed carbon.  Presumably you can use these CNTs as fuel in a direct-carbon fuel cell as well as building material.  Voila, there's your peaking generation.

Let's see:  $660/ton carbon @ 32.75 GJ/ton @ .85 efficiency =$85.35/MWh fuel cost.  Not too shabby.  I think we might have a winner here.

Notice that it includes hypedrogen precisely nowhere?

Superb.
This could be an alternative for steel in many applications.
Among those reinforced concrete.

We have to be carefull though. I dont know how these CNT's behave in the biosphere.
They have properties in common with asbestos : fibrous, catalytically active, chemically very inert.
This should be evaluated before.

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