A COMPARATIVE-STUDY OF NIO(LI), LIFEO2, AND LICOO2 POROUS CATHODES FOR MOLTEN-CARBONATE FUEL-CELLS

Porous cathodes of NiO(Li), Co-doped LiFeO2, and LiCoO2 for the molten carbonate fuel cell (MCFC) were examined in a comparative study using electrochemical impedance spectroscopy at temperatures of 923, 973, a nd 1023 K. Using this technique the contributions of charge transfer a nd diffusion to the impedance could be separated. The impedance result s as a function of gas composition were compared with theoretical pred ictions using the thin-film model leading to the conclusion that the m ost predominant diffusing species in porous MCFC electrodes are molecu lar oxygen and carbon dioxide. The reaction mechanism is probably the same for all three cathodes involving either the reduction of peroxyca rbonate or the reduction of dissociated oxygen. The remaining differen ce in gas dependencies can then be explained by assuming a low coverag e of oxide ions on LiFeO2 while NiO(Li) and LiCoO2 have intermediate c overage by oxide ions. From the temperature dependence of the impedanc e an estimate may be given of the activation energies of the polarizat ion processes.