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

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 CO2 tolerance ability. In this work, iron-based perovskite materials Bi0.5Sr0.5Fe1-xTaxO3-delta 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, Bi0.5Sr0.5Fe0.9Ta0.1O3-delta exhibits the highest electrochemical performance with the lowest polarization resistance (R-p) of 0.12452 Omega cm(2) at 700 degrees C in air. The peak power density of the single cell with Bi0.5Sr0.5Fe0.9Ta0.1O3-delta cathode reaches 1.36 W cm(-2) at 700 degrees C. Compared to Bi0.5Sr0.5FeO3-delta, the improved CO2 tolerance of Ta-doped oxides can be attributed to the high acidity of Ta5+ 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 Bi0.5Sr0.5Fe0.9Ta0.1O3-delta cathode.