Cathodic reaction kinetics for CO₂ capture and utilization in molten carbonates at mild temperatures

Electrochemical reduction of CO₂ to value-added carbon and oxygen in molten carbonates is a promising approach to the efficient and economical utilization of CO₂. Fully understanding the electrode kinetics is crucial to scaling up the process. Herein, the reduction kinetics were studied by cyclic voltammetry, linear sweep voltammetry and potentiostatic electrolysis. The electrolytic products prepared at selected potentials were characterized by X-ray diffraction. It was found that the cathode surface was partially covered by insoluble lithium oxide and that the sluggish diffusion of the O^2– ion was the rate-determining step during carbon deposition at 723 K. When the temperature is increased to 923 K, the reaction kinetics are accelerated around 100-fold with a limiting current density of 1.5 A/cm². Knowledge of this mechanism should prove useful in the design of a pilot cell based on molten salt CO₂ capture and electrochemical transformation (MSCC-ET) technology.