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

Abstract

The SOS-CO₂ 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 O₂/CO₂ mixtures with up to 79 % v/v CO₂. The durability of 25 cm² anode-supported SOFCs (SolydEra) with LSM-YSZ/LSM (La_0.8Sr_0.2MnO_3-δ-Y_0.16Zr_0.92O_2+δ/La_0.8Sr_0.2MnO_3-δ) cathodes was evaluated for more than 1500 h, at 1 atm, 700 °C, and 0.85 V, with 7 % humidified H₂ and a methane-based reformate as the fuel, and with either air or a 21/79 O₂/CO₂ mixture as the oxidant. Compared to the air supply, the performance of the SOFC (303 mW/cm² with humidified H₂ and 155 mW/cm² with reformate, at 0.85 V) remained unaltered when CO₂ was fed, making the LSM-YSZ/LSM cathode ideal for the SOS-CO₂ application. The occurrence of an activation process when the SOFC was operated under prolonged current extraction (from 65 to 447 mW/cm² 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.