IMPEDANCE ANALYSIS FOR OXYGEN REDUCTION IN A LITHIUM-CARBONATE MELT - EFFECTS OF PARTIAL-PRESSURE OF CARBON-DIOXIDE AND TEMPERATURE

Effects of partial pressure of carbon dioxide and temperature on oxygen reduction kinetics on a gold electrode in a lithium carbonate melt were examined using electrochemical impedance spectroscopic (EIS) and linear sweep voltammetric techniques. The impedance spectra were analyzed by a complex nonlinear least squares method, using the Randles-Ershler equivalent circuit model, to determine the electrode-kinetic and the mass-transfer parameters such as the charge-transfer resistance and the Warburg coefficient. The cyclic voltammetric measurements indicated that the oxygen reduction process in lithium carbonate melt is ''reversible'' up to 200 mV/s. The product D(o)1/2C(o) determined by cyclic voltammetry agreed well with those estimated by the EIS method. The reaction order with respect to carbon dioxide and the activation energy for the exchange current density were determined to be -0.52 and 132 kJ/mol, respectively Also, the reaction order with respect to carbon dioxide and the activation energy for D(o)1/2C(o) were calculated to be -0.8 and 185 kJ/mol, respectively