Electrochemical performance of LSM-YSZ SOFC cathodes: activation, durability, and tolerance to CO2

The SOS-CO 2 cycle, a hybrid cycle that combines a pressurized solid oxide fuel cell (SOFC) with an oxy-turbine cycle, requires the SOFC's cathode to operate with O 2 /CO 2 mixtures with up to 79 % v/v CO 2 . The durability of 25 cm 2 anode-supported SOFCs (SolydEra) with LSM-YSZ/LSM (La 0.8 Sr 0.2 MnO 3-δ -Y 0.16 Zr 0.92 O 2+δ /La 0.8 Sr 0.2 MnO 3-δ ) cathodes was evaluated for more than 1500 h, at 1 atm, 700 °C, and 0.85 V, with 7 % humidified H 2 and a methane-based reformate as the fuel, and with either air or a 21/79 O 2 /CO 2 mixture as the oxidant. Compared to the air supply, the performance of the SOFC (303 mW/cm 2 with humidified H 2 and 155 mW/cm 2 with reformate, at 0.85 V) remained unaltered when CO 2 was fed, making the LSM-YSZ/LSM cathode ideal for the SOS-CO 2 application. The occurrence of an activation process when the SOFC was operated under prolonged current extraction (from 65 to 447 mW/cm 2 at 0.7 V after 140 h) was observed. The effectiveness of this process depended on the thermal history of the SOFC. A short-term enhancement of the current density was also observed, as a hysteresis loop affecting the I/V curves. XPS and XRD analyses suggested that these phenomena were associated to modifications of the LSM-YSZ/LSM cathode's surface. • A SolydEra SOFC (25 cm 2 ) was tested for 1575 h with humidified H 2 and reformate. • The LSM-YSZ/LSM cathode's R pol decreases under prolonged polarization (over 140 h). • The increase of cathode performance was correlated with the reduction of Mn ions. • A hysteresis loop characterizes the I/V sweeps of SOFCs based on LSM-YSZ/LSM. • No power reduction occurs passing from cathodic air to 21 % O 2 79 % CO 2 at 700 °C.