Electrochemical characterization of PrBa2−xSrxCu3O6+δ layered oxides as innovative and efficient oxygen electrode for IT-SOFCs

PrBa2Cu3O6+δ (P) and PrBa1.5Sr0.5Cu3O6+δ (PS) layered perovskite-type oxides are synthesized and characterized as oxygen electrodes in IT-SOFCs. The layered structure of P and PS compounds is constituted by the regular alternation along the crystallographic c axis of Pr-O planes, Cu2+ chains (CN = 4) and Cu3+ pyramidal (CN = 5) layers. Interesting features of the PrBa2Cu3O6+δ structure are the absence of cobalt, the presence of aliovalent cations and large amounts of oxygen vacancies. The substitution of 25% Ba with Sr is evaluated in order to improve the electronic conductivity of the undoped material. The compounds are synthesized via Citrate-Nitrate procedure and characterized by XRPD, 4-probe conductivity tests (100-800 °C) and EIS measurements on symmetric cells in air varying the temperature (450-850 °C). SEM images of post mortem cells are collected to evaluate the adhesion between components, layers thickness and particle morphology. Sr doping does not significantly improve the electrical conductivity but prompts a considerable hysteresis in the P sample between the cooling and the heating ramps. Conductivity values are lower than 100 S cm-1, but no electrical limitations are observed in EIS results. The introduction of a thin PrDC interlayer greatly reduces the Area Specific Resistances for both the compounds and the 0.15 Ω cm2 target is almost fulfilled at 600 °C (0.17 Ω cm2 for PS+PrDC sample).