Ta-doped PrBa0.94Co2-xTaxO5+δ as promising oxygen electrodes: A focused study on catalytic oxygen reduction reaction activity, stability and CO2-durability

Abstract

A promising perspective on development of solid oxide fuel cells (SOFCs) is to design a stable oxygen electrode with high catalytic activity toward oxygen reduction reaction (ORR) at reduced temperature. In this study, a series of layered perovskite PrBa0.94Co2-xTaxO5+δ (x = 0–0.04) oxides are systematically studied as oxygen electrodes for intermediate-temperature SOFCs (IT-SOFCs). It is demonstrated that the substitution of Ta5+ for the cobalt ions not only can stabilize the A-site ordered layered structure, but also can improve significantly the catalytic activity for ORR. High electrical conductivity and fast surface oxygen kinetics of the PrBa0.94Co2-xTaxO5+δ cathodes may be responsible for their excellent electrochemical performance. The optimal composition, 2 mol % Ta5+-doped PrBa0.94Co1.96Ta0.04O5+δ, exhibits a lowest polarization resistance (0.020 Ω cm2 at 700 °C). The single cell with the PrBa0.94Co1.96Ta0.04O5+δ cathode delivers a peak power density of 1050 mW cm−2 at 700 °C and is operated steadily at a loading voltage of 0.6 V over 100 h at 650 °C. Furthermore, the PrBa0.94Co1.96Ta0.04O5+δ cathode shows an excellent tolerance to CO2, as evidenced by a durable polarization resistance of 0.061 Ω cm2 at 700 °C in air with 10 vol % CO2.