Scandium-doped PrBaCo2−xScxO6−δ oxides as cathode material for intermediate-temperature solid oxide fuel cells

Scandium-doped PrBaCo2−xScxO6−δ(PBCS-x, x = 0.00–1.00) oxides have been evaluated as cathode materials of intermediate-temperature solid oxide fuel cells (IT-SOFCs) with respect to phase structure, oxygen content, thermal expansion behavior and electrical and electrochemical properties. The XRD results have demonstrated a phase transition in PBCS-x due to Sc3+ doping from tetragonal double-layered perovskite structure at x = 0.00–0.20, bi-phase mixtures at x = 0.30–0.40, to cubic perovskite structure at x = 0.50–0.90. The oxygen contents (6-δ) and average valences of cobalt ions in PBCS-x decrease with the higher Sc3+ content and increasing temperatures in air. Sc3+ doping has also led to decreased thermal expansion coefficients, lowered electrical conductivities and enhanced electrochemical reaction activities for PBCS-x characterized by decreased area-specific resistances (ASRs) and smaller reaction activation energies. Among the studied samples, the PBCS-0.50 oxide with Sc3+-doping content of x = 0.50 exhibits the best electrochemical performance on Ce0.9Gd0.1O1.95 electrolyte. Its ASR values range from 0.123 Ω cm2 at 600 °C to 0.022 Ω cm2 at 750 °C, which are much lower than the related cathode materials. These results have demonstrated that the PBCS-0.50 oxide is a promising cathode material for IT-SOFCs.