Carbon Nanotubes Electrosynthesized from CO2 for Efficient Greenhouse Gas Removal
Authors: Licht Stuart , Ren Jiawen , Lefler Matthew J. , Johnson Marcus , Vicini Juan 
Published: February 2020

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

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

Figure 1