ELECTRODE-KINETICS OF OXYGEN REDUCTION ON GOLD IN MOLTEN CARBONATE

The kinetics of oxygen reduction on gold in pure Li2CO3 and Li + K carbonate eutectic melts were studied using various techniques. The steady-state current in the potentiostatic mode was very agitation-dependent, indicating that the mass transfer effect was significant even at low polarization. The stability limits of the carbonate melt and the reaction sequence of oxygen reduction were examined by the potential scan method. The kinetic parameters were determined using the potential step method. The exchange current density was found to be two orders of magnitude higher than the value suggested by potential scan measurements. The standard exchange current density in the eutectic is 11.0 mA/cm2 at 650-degrees-C; that in pure Li2CO3 at 750-degrees-C is 26.3 mA/cm2. The exchange reaction orders of O2 and CO2, which are similar in the two melts, are quite different from the theoretical values according to the peroxide or superoxide mechanisms. The slow neutralization reaction of oxide by CO2, which has a strong effect on the electrode potential, is the main reason for this discrepancy.