THE EXCHANGE CURRENT-DENSITY OF OXIDE CATHODES IN MOLTEN CARBONATES

The exchange current density (i0) for oxygen reduction has been measur ed by using a potential step technique on nonporous oxide electrodes i n an Li/K(62/38 mole percent) carbonate eutectic melt at 923 K. Nonpor ous oxides were fabricated by a hot isostatic pressing method to be as dense as possible to study the kinetic parameters of the oxygen reduc tion on smooth oxide electrodes. However, the nonporous oxides had sli ghtly rough surfaces. Accordingly, to allow for electrode roughness, t he area of the nonporous oxide electrodes were corrected from the doub le-layer capacity values to make a comparison between our nonporous ox ide electrodes and those used by other researchers. Results were obtai ned on Li0.1Ni0.9O, LiFeO2, LiCoO2, and Au electrodes under p(O2)/p(CO 2) = 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 cu rrent density was as follows: 74 mA/cm2 on Li0.1Ni0.9O, 9 mA/cm2 on Li FeO2, 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.