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

Abstract

Bismuth is doped to lanthanum strontium ferrite to produce ferrite-based perovskites with a composition of La(0.8-x)Bi(x)Sr0.2FeO(3-δ) (0 ≤ x ≤ 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 (K(chem)), and chemical diffusion coefficient (D(chem)) are explored as a function of bismuth content. While σ decreases with x due to the reduced Fe(4+) content, D(chem) and K(chem) 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(2) at 700 °C with Bi doping. The perovskite with x = 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.

La0.4Bi0.4Sr0.2FeO3-δ as Cobalt-free Cathode for Intermediate-Temperature Solid Oxide Fuel Cell

“…La0.4Bi0.4Sr0.2FeO3-δ (LBSF) powder was synthesized using a combustion process and the specific fabrication details were previously reported. 8 All chemicals used in this work were from Sinopharm Chemical Reagent Co. Ltd. The combustion agents were ethylenediaminetetraacetic acid (EDTA, 99.5%) and citric acid (99.5%) while the precursors were La2O3 (99.99%), Bi(NO3)3•5H2O (99.0%), Sr(NO3)2 (99.5%), and Fe(NO3)3•9H2O (98.5%).…”

“…[5][6][7] For example, the chemical surface oxygen exchange coefficient (Kchem) is 3.0 × 10 -5 cm s -1 for La0.8Sr0.2FeO3-δ, much higher than 1.0 × 10 -9 cm s -1 for La0.8Sr0.2MnO3-δ at the same temperature, 700 °C. [8][9] In addition, the ferrite materials are much more cost effective and have exhibited higher durability than the cobalt-containing mixed ionic and electronic conductors such as La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and…”

“…8,16 Recently, Bi 3+ is proposed to dope to the A-site in the ferrite to increase the catalytic activity due to the existence of highly polarizable 6s 2 lone pair electrons for Bi 3+ . 8,[17][18][19] In a series of components La0.8-xBixSr0.2FeO3-δ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8), we have demonstrated that the composition La0.4Bi0.4Sr0.2FeO3-δ (LBSF) has exhibited the promising properties for ORR. The Kchem at 700 °C for LBSF is 9.5 × 10 -4 cm s -1 , even higher than 2.8 × 10 -4 cm s -1 for LSCF in the oxygen partial pressure range from 0.05 bar to 0.21 atm.…”

Cobalt‐Free Perovskite Cathodes for Solid Oxide Fuel Cells

“…Among various Co‐free perovskite cathodes summarized in this review, Nb‐doped cathodes mostly show promise considering their lower polarization resistances relative to other cathode compositions. Table shows the rankings for Co‐free perovskite cathodes with polarization resistances below 0.10 Ω cm −2 at 700 °C –––. The polarization resistance of other Co‐free perovskite cathodes however should be further decreased, to at least below a target polarization resistance value of 0.15 Ω cm −2 (below 550 °C) specified by Steele et al.…”

Cobalt‐free perovskite SrTa 0.1 Mo 0.1 Fe 0.8 O 3‐ δ as cathode for intermediate‐temperature solid oxide fuel cells

“…x Bi x Sr 0.2 FeO 3-δ 20 have been widely investigated as cathodes of SOFC. In comparision with cobalt-based perovskite cathodes, those iron-based perovskites have many advantages, such as more stable, moderate TECs, inexpensive and abundant reserves of iron.…”