In the SOS–CO2 cycle, a novel hybrid cycle for blue power production, the solid oxide fuel cell's (SOFC) cathode is supplied with a CO2-rich oxidizing stream (e.g., 21 % O2 79 % CO2 vol.). The durability of state-of-the-art anode-supported SOFCs (25 cm2, SolydEra) with LSCF-GDC/LSC (La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O3+δ/La0.6Sr0.4CoO3+δ) cathodes was tested at atmospheric pressure for 1090 h with 7 % humidified H2 and reformate, at 700 °C and 0.85 V. The SOFC performance was investigated with periodic I/V curves and electrochemical impedance spectroscopy (EIS) measurements. The results highlighted a 24 % power density loss when air was replaced with the O2/CO2 mixture (672 mW/cm2 in air vs. 508 mW/cm2 in O2/CO2 with humidified H2). A stable power output was observed, and complete reversibility was found when the air supply was restored. A distribution of relaxation times (DRT) analysis of the EIS spectra allowed to extract an anodic rate equation for the hydrogen oxidation reaction (HOR) and evaluate the frequency region affected by cathodic CO2. The kinetic effect of CO2 was also studied via EIS on symmetric button cells at varying O2 and CO2 amounts, and a power-law rate equation was derived. The results verify the feasibility of the SOS–CO2 cycle feed conditions at 700 °C and atmospheric pressure.