The characteristics of solid oxide fuel cell (SOFC) cathodes, prepared by infiltration of La0.8Sr0.2FeO3−δ (LSF) into porous yttria-stabilized zirconia (YSZ) scaffolds, were evaluated by studying the effect of p(O2) and of Al2O3overlayers deposited by Atomic Layer Deposition (ALD) on impedance spectra at 873 and 973 K. The electrode resistance of LSF-YSZ composites calcined at 1123 K was dominated by high-frequency processes that show a relatively weak p(O2) dependence of −0.2 at 973 K. Composites calcined to 1373 K exhibited additional, low-frequency features in their impedance spectra that were more strongly dependent on p(O2), −0.43. These low-frequency processes are due to O2 adsorption limitations caused by the lower surface area of the LSF phase. Decreases in the exposed LSF surface caused by ALD films caused similar changes in the impedance spectra. The ALD overlayers were disrupted by heating to 1073 K and electrode polarization at 873 K. The implications of these results for understanding O2 adsorption limitations on SOFC cathodes are discussed.