Kinetics of Oxygen Reduction in Molten Alkali Carbonates under Pressurized Air / CO2 Oxidant Gas Conditions

Abstract

The electrode kinetics and mechanism of oxygen reduction at gold electrodes in (53 + 47) mol % (Li + Na)CO3, (62-38) mol % (Li + K)CO3 and (43.5 + 31.5 + 25) mol % (Li + Na + K) CO3 melts have been investigated under pressurized Air / CO2 oxidant gas conditions in a temperature range of 823-973 K. The total pressure was changed from 1.0 to 5.0 atm with a constant ratio of Air / CO2 = 70 / 30, 80 / 20, 90 / 10 or 95 / 5. It was observed that the oxygen reduction current in cyclic voltammograms increased with the total pressure, indicating that the concentration of reactive species increased. The analyses of the gas partial pressure dependence on Warburg coefficients, which were obtained by ac impedance measurements, revealed that the reaction process in the tested conditions was dominated by the mixed diffusion of Superoxide ion O2 - and dissolved CO2.