Effect of DC current polarization on the electrochemical behaviour of La2NiO4+δ and La3Ni2O7+δ-based systems

The electrode performance of La2NiO4 and La3Ni2O7 as cathode materials for solid oxide fuel cells (SOFC) was analyzed. The study was focused on the electrode polarization resistance of the interfaces formed by the cathodes with Ce0.8Sm0.2O2-delta+2%Co electrolyte. The study was extended to cathodes based on La2NiO4-Ce0.8Sm0.2O2-delta composite and Pt to analyze the effect of changing the electronic and/or ionic transport properties on the electrode interface resistance. The electrode performance was studied in open circuit conditions and with DC current polarization. Important differences in the performance of the pure cathode materials were obtained as function of DC current flux. However, in La2NiO4-Ce0.8Sm0.2O2-delta composite the DC current flux produces minor changes in the electrode polarization resistance. The aging process also affects the OCV electrode performance of cathodes based on Pt and pure ceramics. whereas the effect is practically invaluable in La2NiO4-Ce0.8Sm0.2O2-delta composite. The electrode performance is higher for the composite cathode compared to pure ceramic electrodes for OCV or for low values of DC polarization. However, the important decrease in the interface resistance obtained for high values of DC current flux for La2NiO4 and La3Ni2O7 cathodes increases their electrode performances to values close to those obtained in La2NiO4-Ce0.8Sm0.2O2-delta composite. This retains the cathode overpotential with values as low as 140 mV at 750 degrees C for values of current load of 530 mA cm(-2) for both pure and composite La2NiO4-based cathodes. The low cathode overpotential allows to estimate values of power density between 300 and 350 MW cm(-2) at 750 degrees C for La2NiO4, La3Ni2O7 and La2NiO4-Ce0.8Sm0.2O2-delta composite, operating with Ce0.8Sm0.2O2-delta+2%Co electrolyte, with 300 mu m in thickness, and a Ni-Ce0.8Sm0.2O2-delta cermet anode with H-2 as fuel. (C) 2008 Elsevier B.V. All rights reserved.