A molten calcium carbonate mediator for the electrochemical conversion and absorption of carbon dioxide

Abstract: Electrochemical valorization of CO2 is the key to closing the carbon cycle and achieving global sustainability. High-temperature molten salts are an excellent electrolyte to entail redox reactions at a rapid rate without using rationally designed nano-structured catalysts. However, the large-scale electrolyzer is constrained by expensive and resource-deficient lithium salts. Employing earth-abundant CaCO3 releases the pressure of using strategic lithium resources, but the low solubility of CaO in molten carbonates disables the capability of capturing CO2. In addition, the separation of carbon from water-insoluble CaO and CaCO3 consumes a large amount of acids. To tackle these challenges, we report a CaCO3-containing molten carbonate electrolyzer to prevent the use of lithium salt, and a molten CaCl2 dissolver to separate carbon from CaO that is soluble in molten CaCl2 and can capture CO2 by carbonization. More importantly, we develop a salt-soluble-to-water-insoluble approach to producing ultrafine CaCO3 by using molten salt as a soft template. Overall, this paper opens a pathway to use the cheap and earth-abundant molten CaCO3 as a mediator to converting CO2 to oxygen at a cost-effective inert anode, value-added carbon at the cathode, and ultrafine CaCO3 thorough a salt-to-solution process.