Thermodynamic studies of some composite cathodes used in SOFC

When searching improved cathode materials for use in solid oxide fuel cells (SOFC), a thorough knowledge of the thermodynamics of the new materials is very important. The solid-oxide electrolyte galvanic cell method was selected to study the thermodynamic properties of some composite materials based on lanthanum strontium ferrite manganite, so that the better accuracy of this technique could be fruitfully exploited. The relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium oxygen pressures are obtained in the temperature range of 1073-1273 K. By solid state coulometric titration, the initial composition of the perovskite phases was altered under controlled conditions. The variation of the thermodynamic properties with the oxygen relative stoichiometry change is discussed. The results evidence the influence of the iron content on the thermodynamic properties.