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

Abstract

High-temperature molten salts are an excellent electrolyte to bring about redox reactions at a rapid rate without using rationally designed nano-structured catalysts. However, the large-scale electrolyzer is constrained by the use of expensive and resource-deficient lithium salts. Using 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 salts, 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 for producing ultrafine CaCO₃ using molten salt as a soft template. Overall, this study opens a pathway to use cheap and Earth-abundant molten CaCO₃ as a mediator to convert CO₂ to oxygen at a cost-effective inert anode, with value-added carbon at the cathode, and ultrafine CaCO₃ through a salt-to-solution process.