Structural, transport, thermal, and electrochemical properties of (La1−xSrx)2CoO4±δ cathode in solid-oxide fuel cells.

Layered perovskite (La1−xSrx)2CoO4±δ (x = 0.3, 0.4, 0.5) oxides were prepared using sol–gel route and evaluated as the cathode materials for intermediate-temperature solid-oxide fuel cells. (La1−xSrx)2CoO4±δ has a tetragonal structure with space group of I4/mmm in all cases of x levels. The average thermal expansion coefficient of (La1−xSrx)2CoO4±δ is relatively low and slightly increases with x, which can be ascribed to the sway of Sr doping on the spin-state transition of Co ions. X-ray photoelectron spectroscopy and thermogravimetric analysis show that Co ions exist in mixed oxidation states, but the lattice oxygen content considerably varies with x. Regarding transport property, (La1−xSrx)2CoO4±δ behaves like a semiconductor in the temperature range of 200–800 °C, and the electrical conductivity significantly increases with x. As one of the most important results, electrochemical performance of (La1−xSrx)2CoO4±δ cathode is affected by x in a complex manner, and x = 0.4 cathode, i.e., La1.2Sr0.8CoO4±δ, has the most favored area-specific resistance of 0.062 Ω cm2 and the highest power density of 630 mW cm−2 in an electrolyte-supported single cell at 800 °C, showing a rapid kinetics toward oxygen reduction reaction. This study demonstrates that the structural, transport, thermal, and electrochemical properties of (La1−xSrx)2CoO4±δ cathodes significantly depend on the La/Sr ratio at the A-site of lattice. Rietveld refinement profile and temperature-dependent electrochemical performance for La1.2Sr0.8CoO4±δ cathode material [ABSTRACT FROM AUTHOR]