The cost and practicality of greenhouse
gas removal processes,
which are critical for environmental sustainability, pivot on high-value
secondary applications derived from carbon capture and conversion
techniques. Using the solar thermal electrochemical process (STEP),
ambient CO2 captured in molten lithiated carbonates leads
to the production of carbon nanofibers (CNFs) and carbon nanotubes
(CNTs) at high yield through electrolysis using inexpensive steel
electrodes. These low-cost CO2-derived CNTs and CNFs are
demonstrated as high performance energy storage materials in both
lithium-ion and sodium-ion batteries. Owing to synthetic control of
sp3 content in the synthesized nanostructures, optimized
storage capacities are measured over 370 mAh g–1 (lithium) and 130 mAh g–1 (sodium) with no capacity
fade under durability tests up to 200 and 600 cycles, respectively.
This work demonstrates that ambient CO2, considered as
an environmental pollutant, can be attributed economic value in grid-scale
and portable energy storage systems with STEP scale-up practicality
in the context of combined cycle natural gas electric power generation.
One pathway to remove the greenhouse gas carbon dioxide to mitigate climate change is by dissolution and electrolysis in molten carbonate to produce stable, solid carbon. This study determines critical knowledge to minimize the required electrolysis energy, the reaction stoichiometry in which carbon and O 2 are the principal products, and that CO 2 can be electrolyzed inexpensively. Thermochemical and experimental results indicate that the principal carbon-deposition reaction in molten Li 2 CO 3 or Li 2 O/Li 2 CO 3 electrolytes at 750°C is Li 2 O + 2CO 2 → Li 2 CO 3 + C + O 2 . The reaction occurs at high Faradaic efficiency of the 4e − reduction of CO 2 to carbon and oxygen at an electrolysis voltage as low as <1 V. Electrolytes without lithium carbonate but containing calcium and/or barium carbonate can also be employed as reaction media for successful carbon deposition, e.g. in an Na/BaCO 3 melt. However, the electrolysis reduction in pure Na or K or Na/K carbonate eutectics at 1 atm of CO 2 forms metals and/or gases, i.e., CO.
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