High performance BaFe_1−xBi_xO_3−Δ as cobalt-free cathodes for intermediate temperature solid oxide fuel cells

Bi₂O₃ doped BaFeO_3−δ on the B-site as a cobalt free perovskite cathode for intermediate temperature solid oxide fuel cells is evaluated. The BaFe_1−xBi_xO_3−δ (BFBx) powders are synthesized by solid state reaction. It is found that Bi₂O₃ doping stabilizes the BaFeO₃ cubic phase. The new cathode is compatible with Gd_0.1Ce_0.9O_1.95 even calcined at 1000 °C for 10 h. The electronic conductivity shows a transformation from semiconductor to metal conductor, and achieves its maximum value of 28.1 S cm⁻¹ for BFB10 at 800 °C. The δ is as high as 0.408 for BFB10 determined by iodometric titration. This leads to the free volume in crystal lattice of BFB10 21.60% higher than that of BaNb_0.05Fe_0.95O_3−δ. The area specific resistance is only 0.133 Ω cm² for BFB10 at 750 °C and the average TEC is 26.697 × 10⁻⁶ K⁻¹ measured from room temperature to 800 °C. The peak power density of Ni-YSZ|YSZ|GDC|BFB10 cell is 646.28 mW cm⁻² at 750 °C, higher than that of single cell using LSCF as cathode. These show that BFBx perovskite oxides with cubic phase are promising cathodes for intermediate temperature solid oxide fuel cells.