The solid oxide fuel cell single cells with porous cathodes prepared at various sintering temperatures, having remarkable differences in micro/meso porosity, were studied using impedance, cyclic voltammetry and chronoamperometry measurement methods. Atomic force microscopy, scanning electron microscopy, focused ion beam-scanning electron microscopy, Brunauer-Emmett-Teller and X-ray diffraction methods were used to describe the cathode material physical and porosity characteristics. It was demonstrated that the porosity and surface area of a cathode strongly depend on the cathode sintering temperature. Influence of single cell working temperature, electrode polarization and oxidant and or fuel partial pressure onto the single cell electrochemical behavior, has been analyzed. Power density vs. current density plots show that the electrical power of single cells depend noticeably on the cathode porosity, O-2 partial pressure in the cathode as well as on H-2 partial pressure in the anode compartment. Impedance data were analyzed in detail, using equivalent circuit fitting as well as difference derivative impedance vs. log frequency plots method. It was concluded that the characteristic time constants for the cathode and anode processes are very similar and the exact separation of the anode and cathode processes characteristics is complicated. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.060211jes] All rights reserved.