Surface modulated B-site doping of PrBa0.5Sr0.5Co2-xFexO5+δ as highly efficient cathode for intermediate-temperature solid oxide fuel cells

Abstract

Layered perovskite oxides (PrBaCo2O5+δ) have gained widespread interest as promising electrodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs) because of their excellent oxygen diffusion and transport performance. However, it remains a great challenge to simultaneously realize thermal match and sufficient operational stability in existing IT-SOFCs. Herein, the layered perovskite PrBa0.5Sr0.5Co2-xFexO5+δ (PBSCFx) with strong oxygen reduction reaction (ORR) activity in half-cell and high power density in single cell was designed by partial substitution of Co with Fe. A systematic and comprehensive elaboration on the composition-structure-property relationships of PBSCFx was proposed. Furthermore, the complex electrochemical behavior of the single cell was investigated using equivalent circuit method (ECM) and distribution of relaxation time (DRT). Impressively, the polarization impedance of PBSCF05 (x = 0.5) is only 0.037 Ω·cm2 (T = 750 °C). The single cell with PBSCF05-GDC as the cathode can reach the maximum power density of 0.996 W/cm2 (T = 800 °C), and exhibits good stability in 216 h of long-term operation (T = 750 °C). The superior electrochemical performance of PBSCF05 is mainly attributed to the reduction of high frequency and intermediate frequency polarization resistance, which corresponds to the enhanced transfer process of oxygen ions, oxygen surface exchange and charge transfer process. This work highlights a simple B-site doping strategy to achieve the thermal match in IT-SOFCs, and furthermore, it expands the opportunities for effective utilization of ECM and DRT technology in the high-performance of IT-SOFCs.