A novel family of Nb-doped Bi0.5Sr0.5FeO3- perovskite as cathode material for intermediate-temperature solid oxide fuel cells

Cobalt-free provskite oxides Bi0.5Sr0.5Fe1−xNbxO3−δ (BSFNx, x = 0.05, 0.10 and 0.15) were prepared and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). In particular, the effects of Nb substitution on phase evolution, thermal expansion behavior and electrochemical performance were systematically investigated. The average thermal expansion coefficient (TEC) of BSFNx decreases from 13.3 × 10−6 K−1 at x = 0.05 to 12.6 × 10−6 K−1 at x = 0.15 within a temperature range of 50–800 °C. Among the BSFNx materials, Bi0.5Sr0.5Fe0.9Nb0.1O3−δ (BSFN0.10) oxide shows the best electrochemical performance. The polarization resistances (Rp) of BSFN0.10 cathode on CGO electrolyte are 0.038, 0.075 and 0.156 Ω cm2 at 700, 650 and 600 °C, respectively. Meanwhile the maximum power densities of the anode-supported single cells are 1.28, 1.54 and 1.34 W cm−2 at 700 °C for BSFNx cathodes with x = 0.05, 0.10, and 0.15, respectively. Furthermore, the relationship study of oxygen partial pressure dependence on Rp indicates that the oxygen reduction reaction (ORR) rate-limiting step is the oxygen adsorption-dissociation on the electrode surface. The desirable electrochemical performance demonstrates that BSFNx oxides are potential cathode materials for IT-SOFCs.