Structural, thermal and electrochemical properties of SrCo0.8Fe0.1Ga0.1O3-δ cathode material for intermediate-temperature solid oxide fuel cells

Abstract

From the viewpoint of intermediate-temperature solid oxide fuel cells (IT-SOFCs) application, except for excellent electrochemical performance, a satisfactory cathode must also meet excellent thermal expansion compatibility with other cell components. Therefore, in order to reduce the thermal expansion coefficient (TEC) value and improve catalytic activity of Sr(Co0.9Fe0.1)O3−δ oxide, we report our effort on perovskite-type Ga3+ doped SrCo0.8Fe0.1Ga0.1O3-δ (SCFG) oxide as cathode material for IT-SOFCs. In this work, SCFG cathode was prepared using an improved sol–gel method and its properties were characterized by powder X-ray diffraction (XRD), X-ray Photoelectron Spectra (XPS), thermal expansion coefficient (TEC), electrical conductivity, and electrochemical impedance spectroscopy (EIS). The SCFG powder showed the expected orthorhombic crystal structure. XPS analysis disclosed multi-valence states of the transition-metal cations in SCFG, i.e., [Sr2+][Co3+/Co4+]0.8[Fe3+/Fe4+]0.1[Ga3+]0.1O3−δ. The maximum conductivity of SCFG was 122 S cm−1 at 800 °C. The average TEC value of the SCFG sample was 12.6 × 10−6 K−1 between room temperature and 1023 K, which is lower than the TEC of Sr(Co0.9Fe0.1)O3−δ cathode and is very similar to the value of the electrolyte. The Rp values of SCFG cathode on Ce0.8Sm0.2O1.9 (SDC) and La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolytes were 0.047 and 0.053 Ω cm2 at 800°C, respectively. The maximum power densities of a single-cell with SCFG cathode on 300 μm thick SDC electrolyte were 504, 335 and 193 mW cm−2 at 800, 750 and 700 °C, respectively. These results indicate that SCFG oxide is a promising cathode material for IT-SOFCs duo to its good thermal expansion match with electrolyte and adequate electrochemical performance.