As the levels of carbon dioxide (CO₂) increase in the Earth’s atmosphere, the effects on climate change become increasingly apparent. With the demand to reduce our dependence on fossils fuels and lower our carbon emissions, a transition to renewable energy sources is necessary. Cost effective large-scale electrical energy storage must be established for renewable energy to become a sustainable option for the future. 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

The carbon molten air battery, presented by our group in late 2013,⁷ as one of a new class of rechargeable “molten air” batteries that utilize a molten electrolyte and a quasi-reversible air electrode,^7-10 is attractive due to its scalability, location flexibility, and construction from readily available resources, providing a battery that can be useful for large scale applications, such as the storage of renewable electricity.

Uncommonly, the carbon molten air battery can utilize carbon dioxide directly from the air:^7,11-18

charging: CO_2(g) → C_(solid) + O_2(g) (1)

discharging: C_(solid) + O_2(g) → CO_2(g) (2)

More specifically, in a molten carbonate electrolyte containing added oxide, such as lithium carbonate with lithium oxide, the 4 electron charging reaction eq. 1 approaches 100% faradic efficiency and can be described as the following two equations:

O^2-_(dissolved) + CO_2(g) → CO₃^2-_(molten) (1a)

CO₃^2-_(molten) → C_(solid) + O_2(g) + O^2-_(dissolved) (1b)

Using carbon formed directly from the CO₂in our earth’s atmosphere, the carbon molten air battery is a viable system to provide large-scale energy storage.

References

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

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

²Licht, Efficient Solar-Driven Synthesis, Carbon Capture, and Desalinization, STEP: Solar Thermal Electrochemical Production of Fuels, Metals, Bleach

Advanced Materials, 47, 5592 (2011).

³Licht, Wu, Hettige, Wang, Lau, Asercion, Stuart, STEP Cement: Solar Thermal Electrochemical Production of CaO without CO₂emission,

Chemical Communications, 48, 6019 (2012).

⁴Licht, Cui, Wang, Li, Lau, Liu, Ammonia synthesis by N₂ and steam electrolysis in molten hydroxide suspensions of nanoscale Fe₂O₃,

Science, 345, 637 (2014).

⁵Cui,  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).

⁶Li, Wang, Licht, Sustainable Electrochemical Synthesis of large grain or catalyst sized iron,

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

⁷Licht, Cui, Stuart, Wang, Lau, Molten Air Batteries - A new, highest energy class of rechargeable batteries,

Energy & Environmental Science, 6, 3646 (2013).

⁸Liu, Li, Cui, Liu , Hao, Guo, Pe. Xu, Licht, Critical advances for the iron molten air battery: A new lowest temperature, rechargeable, ternary electrolyte domain,

J. Materials Chemistry, A, 3, 21039 (2015); ibid, 2, 10577 (2014).

⁹Cui,  Xin, Liu,  Liu,  Hao,  Guo, Licht, Improved cycle iron molten air battery performance using a robust fin air electrode,”

J. Electrochem. Soc., in press (2016).

¹⁰Cui, Xiang, Liu,  Xin, Liu Licht, A novel rechargeable zinc-air battery with molten salt electrolyte,

J. Power. Sources, in press (2017).

¹¹Licht, Cui, Wang, STEP Carbon Capture: the barium advantage,

J. CO₂ Utilization, 1, 58 (2013).

¹²Ren, Li, Lau, Gonzalez-Urbina, Licht, One-pot synthesis of carbon nanofibers from CO₂,

Nano Letters, 15, 6142 (2015).

¹³Ren, 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).

¹⁴Licht, 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).

¹⁵Ren, Lau, Lefler, Licht, The minimum electrolytic energy needed to convert carbon dioxide by electrolysis in carbonate melts,

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

¹⁶Lau, 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).

¹⁷Wu, 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).

¹⁸Ren, Licht, Tracking airborne CO₂mitigation and low cost transformation into valuable carbon nanotubes,

Scientific Reports, 106, 208 (2016).

Figure: Variations of the Molten Battery.