Evaluation of La 2 Ni 0.5 Cu 0.5 O 4+δ and Pr 2 Ni 0.5 Cu 0.5 O 4+δ Ruddlesden-Popper-type layered oxides as cathode materials for solid oxide fuel cells

Abstract La 2 Ni 0.5 Cu 0.5 O 4 and Pr 2 Ni 0.5 Cu 0.5 O 4 Ruddlesden-Popper-type oxides were synthesized by a soft chemistry method and characterized in terms of their crystal structure as a function of temperature, thermal expansion coefficient, oxygen content, transport properties and chemical stability, as well as compatibility in relation to Ce 0.8 Gd 0.2 O 1.9 electrolyte. La 2 Ni 0.5 Cu 0.5 O 4 crystallizes in F 4/ mmm space group, while Pr 2 Ni 0.5 Cu 0.5 O 4 possesses Bmab symmetry. Oxygen nonstoichiometry was determined, showing oxygen excess at room temperature: La 2 Ni 0.5 Cu 0.5 O 4.12 and Pr 2 Ni 0.5 Cu 0.5 O 4.07 , but with only small changes in air up to 850 °C. The obtained TECs are compatible to most commonly used electrolytes. Pr 2 Ni 0.5 Cu 0.5 O 4 possesses relatively good electrical conductivity, exceeding 100 S cm −1 in 300–800 °C. A maximum on the electrical conductivity, present for both materials, correlates well with minimum, observed on Seebeck coefficient characteristics. For Pr 2 Ni 0.5 Cu 0.5 O 4 -based SOFC, maximum power densities exceeding 0.13 W cm −2 at 800 °C were recorded. Despite good performance, stability issues arise from a partial decomposition of the materials at 1000 °C.