Abstract
Conductivity properties such as the impedance contributions of grain, grain boundary, and electrode–material interface of brownmillerite-type Ca2Fe2O5 are studied using alternate current (AC) impedance at different temperatures over a wide range of frequencies. The compound was synthesized at 1000 °C by a solid-state reaction. Powder X-ray diffraction confirmed the pure and single-phase formation. The correlation of the electrical properties with the microstructure of the compound was studied by an AC impedance spectroscopic technique at different temperatures (25–300 °C), which demonstrated the contribution of both the grain (bulk) and grain boundary to the impedance. The frequency-dependent electrical conductivity was used to study the conductivity mechanism. The electric impedance and the frequency at different temperatures supported the suggested conduction mechanism.
Highlights
Since brownmillerites have compositional flexibility and are applicable as oxygen ion conductors in solid oxide fuel cells (SOFC) [1], as a membrane for oxygen separation [2], as an electrocatalyst for oxygen or hydrogen evolution reactions, or a catalyst for hydrocarbon oxidation [3,4], there have been intense studies conducted on them
Ca2 FeO5 has been studied for a wide variety of purposes, such as the production of biodiesel using soybean and Jatropha oils by magnetic CaFe2 O4 –Ca2 Fe2 O5 based catalysts [8], ion conductivity in Li-ion batteries [9], and as an electrocatalyst for oxygen evolution reactions [3]
This paper reports the electrochemical impedance spectroscopy (EIS) study of Ca2 Fe2 O5 for its conductivity mechanism with the frequency-dependent alternate current (AC) impedance to understand its conduction mechanism better
Summary
Since brownmillerites have compositional flexibility and are applicable as oxygen ion conductors in solid oxide fuel cells (SOFC) [1], as a membrane for oxygen separation [2], as an electrocatalyst for oxygen or hydrogen evolution reactions, or a catalyst for hydrocarbon oxidation [3,4], there have been intense studies conducted on them. Due to the long-range defect order, this material has been in focus for oxide ion conductivity and other properties and applications. It is used as a parent compound to study the doping effect on the structure and properties [7]. The electrical properties of brownmillerites were generally studied by measuring the electrical conductivity by the direct current (DC) method or electrochemical impedance method. The DC technique was found to apply to measuring oxide ion conductivity in brownmillerite-type compounds [10,11]. EIS is a powerful tool to measure various electrochemical and electromagnetic properties as well as the charge transport mechanisms It provides information on the grains, grain boundary, and electrode material interface’s contributions to the impedance during charge transport [13,14]. This paper reports the EIS study of Ca2 Fe2 O5 for its conductivity mechanism with the frequency-dependent AC impedance to understand its conduction mechanism better
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