STABILITY AND CHARACTERIZATION OF OXYGEN SPECIES IN ALKALI MOLTEN-CARBONATE - A THERMODYNAMIC AND ELECTROCHEMICAL APPROACH

The stability and electrochemical behavior of reduced oxygen species were investigated in several alkali molten carbonates at different oxoacidity levels and temperatures. Theoretical predictions and experimental results were in good agreement and show that, in Na-K, Li-Na, Li-K, and Li-Na-K melts, peroxide species can only be stabilized in basic media. Superoxide species, unstable in lithium-containing carbonate, can be stabilized in Na-K under slightly basic conditions. Peroxide/oxide and superoxide/oxide redox systems were characterized by voltammetric and convolution potential sweep techniques. It was shown that CO2 does not participate in the rate-determining reduction mechanisms of both superoxide and peroxide species. Electrochemical parameters relative to the cited systems (D, delta, E-degrees, E1/2), as well as the solubility of reduced oxygen species were determined.