Displaying superior strength, conductivity, flexibility and durability, carbon nanotube (CNT) applications had been limited due to the cost intensive complexities of their synthesis. We present an inexpensive, high-yield and scale-able synthesis of CNTs. We show that common metals act as CNT nucleation sites in molten media to efficiently drive the unexpected, high yield electrolytic conversion of CO₂ dissolved in molten carbonates to CNTs. We accomplish this by electrochemically reducing CO₂ on steel electrodes in a molten carbonate electrolyte. The CNT structure is tuned by controlling the electrolysis conditions, such as the addition of trace common metals to act as CNF nucleation sites, the concentration of added oxide, the addition of initiators and the control of current density. The process can be driven by efficient solar, as well as conventional, energy. Scalability of the process is demonstrated from 1 A to 100A. An inexpensive source of CNTs made from carbon dioxide will facilitate the rate of its adoption as an important societal resource for the building, aerospace, transportation, renewable energy, sporting and consumer electronics industries, while concurrently consuming carbon dioxide.

As the levels of carbon dioxide (CO₂) increase in the Earth’s atmosphere, the effects on climate change become increasingly apparent. An incentive to remove the greenhouse gas carbon dioxide is provided by its low energy, low cost, high yield conversion to valuable products such as carbon nanotubes.

We've previously shown that carbon dioxide can be captured directly from the air at solar efficiencies as high as 50%, and that carbon dioxide associated with cement formation and the production of other commodities, such as ammonia and iron, can be electrochemically avoided in the STEP process.^1-6

Here we show the effective capture of CO₂ and its conversion at high yield to carbon nanotubes at low energy and high yield by dissolution in molten carbonates and splitting by electrolysis in molten carbonate to carbon nanotubes and oxygen.^9-15

References

¹Licht, STEP generation of energetic molecules: A solar chemical process to end anthropogenic global warming,

J. Phys. Chem., C, 113, 16283 (2009).

²Licht, Wang, Ghosh, Ayub, Jiang, Ganley, New Solar Carbon Capture Process: Solar Thermal Electrochemical Photo (STEP) Carbon Capture

J. Phys. Chem. Lett, 1, 2363 (2010).

³Licht, Efficient Solar-Driven Synthesis, Carbon Capture, and Desalinization, STEP: Solar Thermal Electrochemical Production of Fuels, Metals, Bleach

Advanced Materials, 47, 5592 (2011).

⁴Licht, Wu, Hettige, Wang, Lau, Asercion, Stuart, STEP Cement: Solar Thermal Electrochemical Production of CaO without CO₂emission,

Chemical Communications, 48, 6019 (2012).

⁵Licht, Cui, Wang, STEP Carbon Capture: the barium advantage,

J. CO₂ Utilization, 1, 58 (2013).

⁶Licht, Cui, Wang, Li, Lau, Liu, Ammonia synthesis by N₂ and steam electrolysis in molten hydroxide suspensions of nanoscale Fe₂O₃,

Science, 345, 637 (2014).

⁷Cui,  Zhang, Liu, Liu, Xiang,  Liu, Xin, Lefler, Licht, Electrochemical synthesis of ammonia directly from N₂ and water over iron-based catalysts supported on activated carbons,

Green Chemistry, 2 DOI: 10.1039/C6GC02386J (2016).

⁸Li, Wang, Licht, Sustainable Electrochemical Synthesis of large grain or catalyst sized iron,

J. Sustainable Metallurgy, 2, 405 (2016).

⁹Ren, Li, Lau, Gonzalez-Urbina, Licht, One-pot synthesis of carbon nanofibers from CO₂,

Nano Letters, 15, 6142 (2015).

¹⁰Ren, Lau, Lefler, S. Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts,

J. Phys. Chem., C, 119, 23342 (2015).

¹¹Licht, Douglas, Ren, Carter, Lefler, Pint, Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes,

ACS Central Science, 2, 162 (2015).

¹²Ren, Lau, Lefler, Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts,

J. Phys. Chem., C, 119, 23342 (2015).

¹³Lau, Dey, Licht, Thermodynamic assessment of CO₂to carbon nanofiber transformation for carbon sequestration in a combined cycle gas or a coal power plant,

Energy Conservation and Management, 122, 400 (2016).

¹⁴Wu, Li, Ji, Liu, Li, Yuan, Zhang, Ren, Lefler, Wang, Licht, One-Pot Synthesis of Nanostructured Carbon Material from Carbon Dioxide via Electrolysis in Molten Carbonate Salts,

Carbon, 6, 27760 (2016).

¹⁵Ren, Licht, Tracking airborne CO₂mitigation and low cost transformation into valuable carbon nanotubes,

Scientific Reports, 106, 208 (2016).

Figure: Molten carbonate electrolysis pathways converting CO₂ leading to a high yield, uniform CNF product.