A New Insight into the Oxygen Reduction Reaction on High Performance Cation-Ordered PBCO Perovskite as IT-SOFC Cathode

The advantage of double perovskite materials (cation-ordered) over single perovskite materials (cation disordered) have been widely reported in SOFC cathode studies. However, the effect of the different phase structures of double perovskite on the electrode performance has not been investigated. In this work, tetragonal and orthorhombic PrBaCo2O5+δ (PBCO) perovskite powders are synthesized through controlling of the sintering atmosphere and temperatures. X-ray diffraction and scanning electron microscopy are used to examine the phase structure and morphology. The bulk diffusion (D) and surface exchange (k) coefficients were characterized by electrical conductivity relaxation (ECR) test on dense PBCO samples. The electrode performance is evaluated by electrochemical impedance spectroscopy (EIS) on symmetric cells. It is found that the tetragonal structure displays smaller polarization resistance than that of the orthorhombic structure. Polarization resistance value at 650 oC are 0.078 Ω·cm2 and 0.10 Ω·cm2 respectively. This tendency is coincident with the higher D and k values obtained from ECR for the tetragonal structure. Oxygen incorporation is suggested as the rate-determining step in the oxygen reduction reaction based on the analysis of EIS and D&k data.