THE EXCHANGE CURRENT-DENSITY OF OXIDE CATHODES IN MOLTEN CARBONATES

The exchange current density (i0) for oxygen reduction has been measured by using a potential step technique on nonporous oxide electrodes in an Li/K(62/38 mole percent) carbonate eutectic melt at 923 K. Nonporous oxides were fabricated by a hot isostatic pressing method to be as dense as possible to study the kinetic parameters of the oxygen reduction on smooth oxide electrodes. However, the nonporous oxides had slightly rough surfaces. Accordingly, to allow for electrode roughness, the area of the nonporous oxide electrodes were corrected from the double-layer capacity values to make a comparison between our nonporous oxide electrodes and those used by other researchers. Results were obtained on Li0.1Ni0.9O, LiFeO2, LiCoO2, and Au electrodes under p(O2)/p(CO2) = 0.9/0.1, p(O2)/p(CO2) = 0. 33/0.67, and p(O2)/p(CO2) = 0.14/0.30 (70% air and 30% CO2) atmosphere. A typical result for the exchange current density was as follows: 74 mA/cm2 on Li0.1Ni0.9O, 9 mA/cm2 on LiFeO2, 11 mA/cm2 on LiCoO2, and 9 mA/cM2 on Au at 923 K under the p(O2)/p(CO2) = 0.9/0.1 atmosphere.