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GWU team develops low-cost, high-yield one-pot synthesis of carbon nanofibers from atmospheric CO2

A team led by Dr. Stuart Licht at The George Washington University in Washington, DC has developed a low-cost, high-yield and scalable process for the electrolytic conversion of atmospheric CO2 dissolved in molten carbonates into carbon nanofibers (CNFs.) The conversion of CO2 → CCNF + O2 can be driven by efficient solar, as well as conventional, energy at inexpensive steel or nickel electrodes.

The structure is tuned by controlling the electrolysis conditions, such as the addition of trace transition metals to act as CNF nucleation sites; the addition of zinc as an initiator; and the control of current density. An open access paper on their work is published in the ACS journal Nano Letters; the work was also presented at ACS’ 250th National Meeting & Exposition this week in Boston.

The synthesis of nano carbon fibers and modified CNFs has been of increasing interest, with applications ranging from capacitors, Li-ion batteries, and electrocatalysts to the principal component of lightweight, high strength building materials; today, CNF demand is mainly limited by the complexity and cost of the synthetic process, which requires 30−100-fold higher production energy compared to aluminum. Carbon nanofibers have been synthesized from a variety of materials including pitch, rayon, polyacrylonitrile, solid carbon materials, acetone, or hydrocarbon gases, by employing electrospinning/carbonization, chemical vapor deposition (CVD), arc/plasma techniques, etc. Recent interests are focusing on renewable feedstocks, i.e., lignin and cellulose, rather than conventional chemicals from the natural gas or petroleum industry.

Here, we synthesize a valuable commodity, CNFs, directly from atmospheric CO2 in a one-pot synthesis. The “production of CNFs by electrolysis in molten lithium carbonate is impossible” according to a prior report in the literature. Yet here, we present exactly that—a high yield process for the electrolytic conversion of CO2, dissolved in molten carbonates, directly to CNFs at high rates using scalable, inexpensive nickel and steel electrodes.

—Ren et al.

Previously, the researchers had made fertilizer and cement without emitting CO2, which they reported. Now, the team, which includes postdoctoral fellow Jiawen Ren, Ph.D., and graduate student Jessica Stuart, says their research make CO2 a feedstock for the manufacture of in-demand carbon nanofibers.

In the process, CO2 is broken down in a high-temperature electrolytic bath of molten carbonates at 750 ˚C (1,380 ˚F). Atmospheric air is added to an electrolytic cell. Once there, the CO2 dissolves when subjected to the heat and direct current through electrodes of nickel and steel. The carbon nanofibers build up on the steel electrode, where they can be removed, Licht says.

To power the syntheses, heat and electricity are produced through a hybrid and extremely efficient concentrating solar-energy system. The system focuses the sun’s rays on a photovoltaic solar cell to generate electricity and on a second system to generate heat and thermal energy, which raises the temperature of the electrolytic cell.

Licht estimates electrical energy costs of this “solar thermal electrochemical process” to be around $1,000 per ton of carbon nanofiber product, which means the cost of running the system is hundreds of times less than the value of product output.

We calculate that with a physical area less than 10% the size of the Sahara Desert, our process could remove enough CO2 to decrease atmospheric levels to those of the pre-industrial revolution within 10 years.

—Stuart Licht

At this time, the system is experimental, and Licht’s biggest challenge will be to ramp up the process and gain experience to make consistently sized nanofibers. Licht said the team is scaling the process up quickly, and soon should be in range of making tens of grams of nanofibers an hour.

One advance the group has recently achieved is the ability to synthesize carbon fibers using even less energy than when the process was initially developed. Carbon nanofiber growth can occur at less than 1 volt at 750 ˚C,—less than the 3-5 volts used in the 1,000 ˚C industrial formation of aluminum, he said.

We hope this will provide motivation to remove carbon dioxide from the air and to mitigate the effects of climate change, and will decrease the cost of carbon composites for lighter weight electric vehicle components, and provide new higher capacity Li-ion anode opportunities for Li batteries.

—Stuart Licht

The team’s research has been funded primarily by the National Science Foundation.

Resources

  • Jiawen Ren, Fang-Fang Li, Jason Lau, Luis Gonzaĺez-Urbina, and Stuart Licht (2015) “One-Pot Synthesis of Carbon Nanofibers from CO2Nano Letters doi: 10.1021/acs.nanolett.5b02427

Comments

Davemart

As a method of making carbon nanotubes, great.
As a way of taking enough CO2 out of the atmosphere to balance global warming at the cost of $1000 ton - they CANNOT be serious!
Utterly barmy.
CO2 reduction typically costs around $50/ton.

ejj

@Davemart: Why are you a denier? This is peer reviewed science, performed at a recognized university (GWU) and funded by the National Science Foundation.

HarveyD

This could become (a costly at first) win-win-win solution to:

1) remove excess accumulated CO2 from the atmosphere.
2) produce large quantities of lower cost CFs.
3) foster the production of clean operation, lighter vehicles/batteries, producing less CO2.

ejj

Why wouldn't the coal companies simply compete directly with the steel companies by making their own carbon fibers from coal?

Davemart

ejj:

Anyone whose currency is loaded polemic like 'denier' is unlikely to understand the issues, including concepts like $1000 being considerably greater than the ~$50 per ton it normally takes to avoid CO2 emissions.

William Stockwell

Davemart, $50 of cost that sequesters a ton of CO2 that brings no other return is much less motivating than spending $1000 a ton and making a product that can be sold for $10,000 a ton.

Engineer-Poet

It'll sell for $10k/ton until the market is saturated.  That is how markets work.  The quantity that can be sold for even $1000/ton is far less than it would take to pull 10 ppm of CO2 out of the atmosphere.

OTOH if these cells can be run as batteries the market would expand massively.  Large amounts of carbon held in inventory in batteries is a distinct possibility.

Gail Tverberg's apocalypse vision is that shortages of materials will cause the collapse of industrial civilization as the energy inputs become unsustainable.  But here we apparently are, with a source of carbon nanofibers for possibly less than a dollar per pound.  CNTs at least can be doped to be as conductive as copper.  If these fibers can be similarly treated (perhaps by doping the carbonate melt) then the replacement for copper and aluminum wiring can literally be pulled out of the air.  At that point there is no possible issue of shortage.

sd

So what could be wrong with this statement?

"We calculate that with a physical area less than 10% the size of the Sahara Desert, our process could remove enough CO2...."

Fun with numbers but did they calculate how much of the world's resources would be consumed by covering 10% of the Sahara Desert with Solar Collectors. Maybe we could just use floating mirrors on the Oceans to beam the sunlight back into space. Of course, we would just burn less coal or maybe even support birth control.

Davemart

EP and SD:

Right on, both of you!

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