Nb-substituted PrBaCo2O5+δ as a cathode for solid oxide fuel cells: A systematic study of structural, electrical, and electrochemical properties

Double perovskite oxides, such as PrBaCo2O5+δ (PBC), are among the most promising cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) thanks to their high catalytic activity and mixed ionic and electronic conductivity. Here, we investigate the impact of Nb substitution on the crystal structure, catalytic activity, and electrical conductivity of PBC. Several studies have outlined that doping high valence cations, such as Nb5+, effectively stabilizes the perovskite structure, decreases the thermochemical expansion coefficient of the material, and can benefit the peak power density of the fuel cell. The as-prepared PrBaCo2−xNbxO5+δ with x = 0, 0.25, 0.50, 0.75, and 1.00 (PBCN) exhibit structural change from P4/mmm (x = 0) to I4/mmm (x = 1), whereas both phases are present for intermediate compositions. The analysis of electrochemical impedance spectroscopy (EIS) data shows that PBCN is characterized by relatively low polarization resistance. Between 300 and 800 °C, the electrical conductivity of PBCN, with x = 0.25, 0.50, lies above 100 S cm−1. If x = 0.75 or 1.00, the conductivity drops below 100 S cm−1. Our work suggests that the Nb-doped PBC exhibits excellent chemical compatibility with typical electrolyte material and good electrochemical performance, making it a promising cathode material for applications in IT-SOFCs.