Structures and Properties of LaFe_0.8Cu_0.2O_3−δ and BaFe_0.8Cu_0.2O_3−δ as Cobalt‐Free Perovskite‐Type Cathode Materials for the Oxygen Reduction Reaction

Abstract

Perovskite oxides with mixed electronic–ionic conduction are important catalysts for the oxygen reduction reaction in solid oxide fuel cells (SOFCs). Here, two cobalt‐free perovskite oxides, LaFe0.8Cu0.2O3−δ (LFCuO) and BaFe0.8Cu0.2O3−δ (BFCuO), were synthesized and comparatively studied with respect to their phase structures, oxygen contents, chemical defects, thermal expansion coefficient (TEC), as well as electrical and electrochemical properties. Different structures and properties have been found for each oxide, which have been interpreted based on their tolerance factors and chemical defects. LFCuO showed much better overall performance than BFCuO, and it proved to be a promising cobalt‐free cathode material of intermediate‐temperature SOFCs with a low TEC (12.0×10−6 °C−1) that matches well with TECs of the electrolytes, high catalytic activity for the oxygen reduction reaction characterized by low area specific resistances (0.090 Ω cm2 at 800 °C and 0.20 Ω cm2 at 750 °C), and high‐temperature chemical stability with electrolytes.

Sr3Fe1.5Zn0.5O7-δ as Cathode for Protonic-Conducting Solid Oxide Fuel Cells with Enhanced Oxygen Reduction Reaction Activity

“…This is attributed to the more abundant oxygen vacancies and electrocatalytic sites. The calculated E a value for SFZ05 is 1.54 eV, also lower than some other Fe-based electrodes (14,15). At 750 °C, the polarization resistance of SFZ05 is 0.072 Ω•cm -2 , which is 47% lower than that of the undoped Sr 3 Fe 2 O 7-δ (SFO), and the peak power density of the single-cell with an SFZ05 cathode reaches 523.56 mW•cm -2 .…”

Effect of calcium doping on the electrocatalytic activity of the Bi1−xCaxFeO3−δ oxygen electrode for solid oxide fuel cells

“…The activation energy ( E a ) values of the BCF0.1, BCF0.2, and BCF0.3 cathodes are 124.4, 110.8, and 122.4 kJ mol −1 , respectively. The lowest E a facilitates the oxygen mobility and electrocatalytic activity of BCF0.2 and is smaller than those of reported Fe-based cathodes, e. g. La 0.8 Ca 0.2 Fe 0.8 Ni 0.2 O 3− δ (178 kJ mol −1 ), 32 LaFe 0.8 Cu 0.2 O 3− δ (159.2 kJ mol −1 ), 37 La 0.5 Sr 0.5 Fe 0.9 Mo 0.1 O 3− δ (146.6 kJ mol −1 ), 38 and PrBaFe 2 O 5+ δ (123.5 kJ mol −1 ). 39…”

Suitability of strontium and cobalt-free perovskite cathodes with La9.67Si5AlO26 apatite electrolyte for intermediate temperature solid oxide fuel cells

“…LFC stands out among the rest of the perovskite compositions. Idrees et al 44 also found low ASRs for this compound as electrode on samarium doped ceria electrolyte. Its areaspecific resistance of 4,3 Ω•cm 2 at 700°C is comparable to other perovskite compositions tested as cathodes with an apatite electrolyte.…”

“…The conductivity of the ferrites shows an abrupt change in activation energy around 500°C. It has been reported for LaFe0.8Cu0.2O3-δ that both Fe 3+ and Fe 4+ coexist at the perovskite B-sites, 44 and thus the oxidation states of Cu and Ni could also change with temperature. This change might be a possible explanation for the abrupt enhancement of conductivity and for LFN and LFC not following the same temperature dependence as the other perovskites in the 300-500°C temperature range.…”

“…Although some studies have already been reported on related manganite, ferrite and chromite compounds, as LaMn1-xNixO3δ, LaFe1-xNixO3-δ, LaCr1-xNixO3-δ 42,43 or LaFe0.8Cu0.2O3-δ, 44 none of these have been tested as cathodes in cells in combination with an apatite electrolyte. The aim of this work is to examine if these compounds satisfy the requirements for acting as cathodes with this electrolyte, including high electronic conductivity, chemical stability in operation conditions, and compatibility with the apatite, both chemical and thermomechanical.…”