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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]

Abstract: We evaluated the performance and durability of platinum-iron-copper with an L10 ordered face-centered tetragonal structure (fct-PtFeCu) as cathode catalysts of membrane-electrode assemblies (MEAs) in polymer electrolyte fuel cells. The exchange current density per unit active surface area of Pt in fct-PtFeCu/C, measured in the MEA, was sufficiently higher than that of commercial Pt/C. The durability of the MEAs was evaluated by three accelerated degradation tests: (1) a load cycle durability test, which mainly accelerates the degradation of catalysts; (2) an open-circuit voltage (OCV) hold test, which mainly degrades membranes; and (3) a hybrid of the load cycle test and OCV hold test. Despite the possible negative effects of dissolved transition metals on the durability of MEAs, fct-PtFeCu/C showed higher durability than commercial Pt/C and at least comparable durability with in-house Pt/C in the OCV hold test, and showed high durability in the hybrid test up to 200 h. These results suggest that the presence of Fe and Cu did not negatively affect the durability of the MEA with fct-PtFeCu/C, and rather the other factor, carbon support, affected more in retaining the durability.Graphical Abstract: [ABSTRACT FROM AUTHOR]