Oxygen reduction mechanism at porous La1-xSrxCoO3-d cathodes/La0.8Sr0.2Ga0.8Mg0.2O2.8 electrolyte interface for solid oxide fuel cells

The oxygen reduction mechanism was investigated at the porous La1-xSrxCoO3- d cathode/ La0.8Sr0.2Ga0.8Mg0.2O2.8, electrolyte interface (x=0.2, 0.3, 0.4 ). The polarization resistance, measured from the impedance spectra, was co mpared in the samples of La1-xSrxCoO3-d as functions of x, temperatures, an d applied DC voltages. The polarization resistance decreased with an increa se of x values in La1-xSrxCoO3-d and with the applied cathodic voltage. The polarization resistance of the higher Sr-concentration in La1-xSrxCoO3-d s howed the lower dependence on cathodic overpotential. The values of the act ivation energy of the interface conductivity (inverse of the polarization r esistance) were similar for all La1-xSrxCoO3-d samples (127-143 kJ mol(-1)) at zero applied voltage (E = 0 V). However, under cathodic polarization, t he activation energy decreased as the applied voltage became more negative, which indicates a change of the reaction mechanism under cathodic polariza tion. Under cathodic polarization, oxide ion diffusion in the bulk La1-xSrx CoO3-d can be one of the main factors determining the reaction rates. (C) 2 001 Elsevier Science Ireland Ltd. All rights reserved.