Enhanced electrocatalytic activity and CO2 tolerant Bi0.5Sr0.5Fe1-xTaxO3-δ as cobalt-free cathode for intermediate-temperature solid oxide fuel cells

Abstract One of the significant motivations in developing intermediate-temperature solid oxide fuel cells (IT-SOFCs) is to design cobalt-free cathodes with high electrocatalytic activity and CO 2 tolerance ability. In this work, iron-based perovskite materials Bi 0.5 Sr 0.5 Fe 1- x Ta x O 3- δ are investigated as potential cathodes for IT-SOFCs. The effects of Ta doping on crystal structure, thermal expansion coefficients and electrocatalytic activities are systematically evaluated. Among the Ta-doped oxides, Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ exhibits the highest electrochemical performance with the lowest polarization resistance ( R p ) of 0.124 Ω cm 2 at 700 °C in air. The peak power density of the single cell with Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ cathode reaches 1.36 W cm −2 at 700 °C. Compared to Bi 0.5 Sr 0.5 FeO 3- δ , the improved CO 2 tolerance of Ta-doped oxides can be attributed to the high acidity of Ta 5+ cations and the increased average metal bond energy (ABE) within the material. Further study proves that the adsorption-dissociation process of molecular oxygen is the limiting step for oxygen reduction reaction (ORR) on Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ cathode.