Electrochemical characterization of PrBa_2-xSr_xCu₃O₆₊ layered oxides as innovative and efficient oxygen electrode for IT-SOFCs

PrBa2Cu3O6+delta (P) and PrBa1.5Sr0.5Cu3O6+delta (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+delta 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 degrees C) and EIS measurements on symmetric cells in air varying the temperature (450-850 degrees 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 Omega cm(2) target is almost fulfilled at 600 degrees C (0.17 Omega cm(2) for PS + PrDC sample).