Oxygen permeability and electrochemical performance of Ca-doped NdBaCo2O5+δ in IT-SOFC

The layered perovskites NdBa _1−xCa _xCo ₂O _5+δ (NBCax, where x = 0.0, 0.1, 0.2, 0.3, and 0.4) have been synthesized through a conventional solid-state reaction and examined as potential cathode candidates for intermediate-temperature solid oxide fuel cells (IT-SOFC; 600 °C–800 °C). The Ca-substituted oxides exhibit a P4/mmm tetragonal structure and a phase transition to simple perovskite at x ≥ 0.3. The electrical conductivity in air at 300 °C–800 °C and oxygen permeation flux of NBCax oxides are influenced by Ca doping content. The activation energy for the oxygen migration process indicates that bulk diffusion is predominant at temperatures below 800 °C. X-ray photoelectron spectroscopy indicates the coexistence of Co ³⁺ and Co ⁴⁺ and oxygen-active sites on the surface of the NBCax oxides. Variations in Co ⁴⁺ and adsorbed oxygen contents are related to the number of oxygen vacancies and are influenced by Ca content. Among the oxides examined, NdBa _0.9Ca _0.1Co ₂O _5+δ exhibits good electrical conductivity, high amounts of Co ⁴⁺ and adsorbed oxygen, high maximum power density of 1286 mW·cm ⁻² at 800 °C in H ₂ fuel in the La _0.9Sr _0.1Ga _0.8Mg _0.2O ₃ electrolyte–supported cell, and low polarization resistance of the cell, as determined using AC impedance spectroscopy. These findings suggest that Ca incorporation can improve the electrochemical performance of NdBaCo ₂O _5+δ , rendering it a promising candidate for use as a cathode material in IT-SOFCs.