Optimization of the interface polarization of the La2NiO4-based cathode working with the Ce1-xSmxO2-δ electrolyte system

The performance of La2NiO4 cathode material and Ce1-xSmxO2-delta (x=0.1, 0.2, 0.3, 0.4) electrolyte system was analyzed. Ceria-based materials were prepared by the freeze-drying precursor route whereas La2NiO4 was prepared by the nitrate-citrate procedure. Electrolyte pellets were obtained after sintering the powders at 1600 degrees C for 10 h. Also dense ceria-based electrolytes samples were obtained by calcining the powders at 1150 degrees C after the addition of 2 mol%-Co. Interface polarization measurements were performed by impedance spectroscopy in air at open circuit voltage, using symmetrical cells prepared after the deposition of porous La2NiO4-electrodes on the Ce1-xSmxO2-delta system. X-ray diffraction (XRD) of cathode materials after using in symmetrical cells confirmed no significant reaction between La2NiO4 and ceria-based electrolytes. The efficiency of the cathode material is highly dependent on the composition of the electrolyte, and low-content Sm-doped ceria samples revealed an important decrease in the performance of the system. Differences in electrochemical behaviour were attributed principally to the oxide ion transference between cathode and electrolyte, and were correlated to the conductivity of the electrolyte. In this way cobalt-doped electrolytes with a Sm-content <= 30% perform better than free-cobalt samples due to the increase in grain boundary conductivity. Finally, composites of the ceria-based materials and La2NiO4 to use as cathode were prepared and an important increase of the interface performance was observed compared to La2NiO4 pure cathode. Predictions of maximum power density were obtained by the mixed transport properties of the electrolytes and by the interface polarization results. The use of composite materials could allow to increase the performance of the cell from 170 mW cm(-2) for pure La2NiO4 cathode, to 370 mW cm(-2) for La2NiO4-Ce0.8Sm0.2O2-delta cathode, both working with Ce0.8Sm0.2O2-delta clectrolyte 300 mu m in thickness and Ni-Ce0.8Sm0.2O2-delta as anode at 800 degrees C. (C) 2007 Elsevier B.V. All rights reserved.