Electrochemical Mechanism of the Carbon Synthesis via Carbonate Ion Electroreduction in Molten Li₂CO₃–K₂CO₃ Mixture

Abstract

As a way to explore methods to capture and transform CO2 into useful carbon materials, the electrochemical mechanism of carbonate ion reduction in molten Li2CO3-K2CO3 eutectic mixtures is studied by cyclic voltammetry, chronopotentiometry, and chronocoulometry.Evidence indicates CO3 2− to undergo reduction to produce solid carbon before the alkali metal ions Li + and K + . The electrode reactions consist of a diffusion-controlled, totally irreversible process comprising a one-step electron transfer. Notably, the described electrochemical process produces carbon sheets, submicron carbon tubes, or submicron carbon particles, depending on the applied cathodic overpotential. When O 2− ions are released as part of the electrochemical reduction of CO3 2− , some of these ions immediately combine with Li + to form insoluble Li2O, which are disadvantageous processes from the standpoint of CO2 capture in the cathodic region.Results suggest thus that a type of molten salt electrolyte in which alkali metal oxides are highly soluble should be employed for effective molten salt CO2 capture and electrochemical transformation.