Electrochemical performance of solid oxide cells with Co-free Sr0.7Ce0.3MnO3-δ-based oxygen electrodes

Strontium-cerium manganite Sr0.7Ce0.3MnO3-δ was evaluated as a Co-free candidate material for oxygen electrodes of commercial-grade solid oxide fuel and electrolysis cells (SOFC/SOEC). Sr0.7Ce0.3MnO3-δ ceramics was confirmed to show high electrical conductivity (304–309 S/cm at 700–800 °C) and moderate thermal expansion coefficient (12.3 ppm/K at 25–1100 °C) at atmospheric oxygen pressure, and very small changes in oxygen nonstoichiometry on p(O2)-T cycling under oxidizing conditions below 1000 °C. The studies of oxygen transport properties by electrical conductivity relaxation technique revealed that, compared to (La,Sr)(Co,Fe)O3-δ perovskites, Sr0.7Ce0.3MnO3-δ exhibits an order of magnitude lower oxygen diffusivity, with Dchem in the range of (4–10) × 10−6 cm2/s at 875–950 °C, but similar oxygen surface exchange kinetics, with kex in the range (0.5–5.6) × 10−3 cm/s at these temperatures. The electrochemical performance of fuel electrode-supported solid oxide cells with Sr0.7Ce0.3MnO3-δ oxygen electrodes at 700–800 °C was found to be moderate but could be improved by surface activation of Sr0.7Ce0.3MnO3-δ electrode layers with praseodymia. The activation of the oxygen electrode resulted in a reduction in total polarization resistance of the cells by 2 and 7 times in SOFC and SOEC modes, respectively, under moderate current densities at 800 °C. The polarization losses in SOFC mode at 700–800 °C were 1.5–2.0 times higher than in the SOEC regime. Further improvements in oxygen electrode performance are necessary to compete with solid electrolyte cells with (La,Sr)CoO3-δ and (La,Sr)(Co,Fe)O3-δ electrodes.