Bismuth Doped Lanthanum Ferrite Perovskites as Novel Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

Bismuth is doped to lanthanum strontium ferrite to produce ferrite-based perovskites with a composition of La<sub>0.8‑x</sub>Bi<sub><i>x</i></sub>Sr<sub>0.2</sub>FeO<sub>3‑δ</sub> (0 ≤ <i>x</i> ≤ 0.8) as novel cathode material for intermediate-temperature solid oxide fuel cells. The perovskite properties including oxygen nonstoichiometry coefficient (δ), average valence of Fe, sinterability, thermal expansion coefficient, electrical conductivity (σ), oxygen chemical surface exchange coefficient (<i>K</i><sub>chem</sub>), and chemical diffusion coefficient (<i>D</i><sub>chem</sub>) are explored as a function of bismuth content. While σ decreases with <i>x</i> due to the reduced Fe<sup>4+</sup> content, <i>D</i><sub>chem</sub> and <i>K</i><sub>chem</sub> increase since the oxygen vacancy concentration is increased by Bi doping. Consequently, the electrochemical performance is substantially improved and the interfacial polarization resistance is reduced from 1.0 to 0.10 Ω cm<sup>2</sup> at 700 °C with Bi doping. The perovskite with <i>x</i> = 0.4 is suggested as the most promising composition as solid oxide fuel cell cathode material since it has demonstrated high electrical conductivity and low interfacial polarization resistance.