The O reduction mechanism of dense mixed-conducting La1−xSrxCo0.2Fe0.8O3−δ electrodes with various Sr contents was investigated by means of alternating-current impedance spectroscopy and potentiostatic current transient techniques. From analyses of the impedance spectra and cathodic potentiostatic current transient, measured as functions of electrode thickness and O partial pressure, it was confirmed that the overall O reduction reaction proceeded mainly by O vacancy diffusion through the electrode, coupled with charge-transfer at the electrode surface. As the Sr content was increased, the decrease in the diffusion resistance, Rd, due to the higher diffusivity of the O vacancy, was more predominant the decrease in the charge-transfer resistance, Rct, due to the larger electrochemically active area, Aea. The smaller values of Rd and Rct, with increasing Sr content, led to a higher initial current, a higher steady-state current and a shorter time to reach a steady-state current in the cathodic potentiostatic current transients. From an analysis of the impedance spectra, combined with cathodic potentiostatic current transients measured on electrodes cathodically polarized for various times, it was deduced that decomposition of SrO at the electrode surface by the cathodic polarization-enhanced Aea resulted in kinetic facilitation of the charge-transfer reaction at the electrode/gas interface.

Mixed Diffusion and Charge-Transfer-Controlled Oxygen Reduction on Dense La1−xSrxCo0.2Fe0.8O3−δ Electrodes with Various Sr Contents. Y.M.Kim, S.I.Pyun, J.S.Kim, G.J.Lee: Journal of the Electrochemical Society, 2007, 154[8], B802-9