Low thermal expansion material Bi_0·5Ba_0·5FeO_3-Δ in application for proton-conducting ceramic fuel cells cathode

The cobalt-free material of Bi³⁺-doped BaFeO_3-δ (BBFO) is synthesized and applied as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with proton conducting electrolyte Ba(Zr_0·1Ce_0·7Y_0.2)O₃ (BZCY). The as-prepared BBFO demonstrates a tetragonal structure with sufficient chemical compatibility, high thermal stability and low thermal expansion coefficient. BBFO exhibits higher electrical conductivity of 4.1 S cm⁻¹compared to the parent material BaFeO_3-δ (BFO) of 3.5 S cm⁻¹. The composite cathode BBFO-BZCY with the mass ratio of 7:3 presents a relatively low R_p of 0.128 Ω cm² at 700 °C in air. According to the oxygen reduction reaction process, the rate-determining step is transformed from charge transfer to oxygen gas (O₂) adsorption-dissociation with the rising temperature. In addition, the performance of the anode-supported cell NiO-BZCY∣BZCY∣BBFO-BZCY is 120 mW cm⁻² as the thickness of electrolyte is 150 μm. It thus promises BBFO as a novel cathode for proton-conducting ceramic fuel cells.