Complex Perovskite system Dy _{0.5‐ x} B a _x Sr _0.5 Co _0.80 Fe _0.20 O _3‐δ : As cathode for IT ‐SOFCs

Abstract The present work is intended to study mixed conductivity of complex perovskite oxide of chemical formula Dy _{0.5‐ x} B a _x Sr _0.5 Co _0.8 Fe _0.2 O _3‐δ ( DBSCF ‐x) (0 ≤ x ≤ 0.07) to check its suitability as cathode for intermediate temperature solid oxide fuel cell ( IT ‐ SOFC s). Low‐temperature sol‐gel combustion route has been used to prepare DBSCF ‐x systems. Structures are confirmed by X‐ray diffraction ( XRD ), exhibit single‐phase perovskite structures with orthorhombic symmetry (space group Pbnm) for all compositions. Thermogravimetry ( TG ) results indicate lattice oxygen loss in Ba‐doped DBSCF system by heat treatment in temperature interval 50‐850°C, which is enhanced in N ₂ atmosphere then air; in contrast to that lattice oxygen, gain is observed for DBSCF ‐0 system. Temperature profile of DC conductivity exhibits metallic behavior of DBSCF ‐x system; however, the DBSCF ‐0 system shows semiconductor‐to‐metal transition at temperature around 450°C. DBSCF ‐0.03 system displays maximum electronic conductivity. Electrochemical performance of electrodes is studied in three‐layer symmetrical cell configuration DBSCF ‐x/Ce _0.85 Sm _0.15 O _2‐δ / DBSCF ‐x by complex impedance spectroscopy ( CIS ). Impedance diagram reveals the presence of three processes mainly associated with (a) diffusion of oxide ions/oxygen intermediates through electrode/electrolyte interface, (b) atomic oxygen diffusion within the electrode, and (c) oxide ion diffusion in the crystal lattice. ASR of the DBSCF ‐0.05 system is found 2.21 ohm cm ² at 700°C, which is lowest amongst all studied compositions. Results show that it is possible to modify the electrochemical properties of the DBSCF ‐x system by changing the composition, but much more work even including optimization of layer thickness and microstructure will be needed to reduce the ASR to the level of the state‐of‐art‐electrodes and thereby better utilize the potential of the DBSCF ‐x system.