Proteic sol-gel synthesis of copper doped misfit Ca-cobaltites with potential SOFC application

The present work reports the synthesis, structure and electrochemical assessment of Cu-doped calcium cobaltites as cathode materials for solid oxide fuel cells (SOFCs). Powders of composition Ca_3−xCu_xCo₄O_9−δ (0 ≤ x ≤ 0.2) were obtained by a proteic sol-gel method which uses gelatin as polymerizing agent. As-prepared materials were calcined at 900 °C for 1 h and characterized by X-ray diffraction, with Rietveld refinement of the diffraction data, and scanning electron microscopy. Screen-printed porous electrodes fired (at 950 °C for 2 h) on both faces of ceria based electrolytes were electrochemically characterized by impedance spectroscopy between 600 and 800 °C in air atmosphere. The results indicated the attainment of Ca_3−xCu_xCo₄O_9−δ solid solutions with monoclinic misfit layered structure and around 2 vol% Co₃O₄ as a secondary phase. Micro-plates like powders had irregular shape and average diameter near 2 μm. The area specific resistance (ASR) is in line with literature data for cathodes of similar compositions prepared by other synthetic routes. ASR was optimized for the composition Ca_2.99Cu_0.01Co₄O_9−δ, achieving 0.84 Ω cm² at 800 °C in air. - Highlights: • Proteic sol-gel synthesis of Ca_3−xCu_xCo₄O_9−δ (0 ≤ x ≤ 0.2). • Cu²⁺ doping enhances electrode densification. • Area specific resistance (ASR = 0.84 Ω cm² at 800 °C) optimized for Ca_2.99Cu_0.01Co₄O_9−δ.