The Minimum Electrolytic Energy Needed To Convert Carbon Dioxide to Carbon by Electrolysis in Carbonate Melts

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 CO2 can be electrolyzed inexpensively. Thermochemical and experimental results indicate that the principal carbon-deposition reaction in molten Li2CO3 or Li2O/Li2CO3 electrolytes at 750 degrees C is Li2O + 2CO(2) -> Li2CO3 + C + O-2. The reaction occurs at high Faradaic efficiency of the 4e(-) reduction of CO2 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/BaCO3 melt. However, the electrolysis reduction in pure Na or K or Na/K carbonate eutectics at 1 atm of CO2 forms metals and/or gases, i.e., CO.