Electrode reaction of La1-xSrxCoO3-d cathodes on La0.8Sr0.2Ga0.8Mg0.2O3-y electrolyte in solid oxide fuel cells

The electrode reaction mechanism was investigated at the porous La1-xSrxCoO 3-d (LSC)/La0.8Sr0.2Ga0.8Mg0.2O3-y (LSGM) interface (x = 0.2, 0.3, 0.4). Di rect current (dc) polarization curves showed a linear relationship between the overpotential and the current density at the lower cathodic polarizatio n. The interface conductivity was adopted to examine the activity for oxyge n reduction at the LSC/LSGM interface, which was measured both from the dc polarization curves and the alternating current impedance. The interface co nductivity increased with Sr concentration in LSC and cathodic applied volt age. The higher Sr concentration of LSC showed the lower oxygen partial pre ssure dependence of the interface conductivity. The activation energy for t he interface conductivity was almost the same for different Sr concentratio n of LSC (137-142 kJ mol(-1)). A similar reaction mechanism is assumed for the examined LSC. The interface conductivity has a relation with oxide ion diffusion in LSC, which can be the main factor to determine the cathode rea ction rates under cathodic polarization. (C) 2001 The Electrochemical Socie ty.