Unlocking High Mixed Ionic-Electronic Conductivity in Bi ₂ MnCoO ₆ : A Promising Electrode for Intermediate-Temperature Solid Oxide Fuel Cells

A bismuth-based double perovskite, Bi 2 MnCoO 6 (BMCO), is synthesized by a conventional solid-state route and is investigated as a potential electrode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction confirms a predominantly single-phase cubic structure with minor secondary phase. Field-emission scanning electron microscopy shows densely packed grains with clean, faceted surfaces and cuboidal-to-polyhedral crystallites, a compact microstructure that minimizes grain-boundary resistance and provides continuous pathways for both electron hopping and oxygen-ion migration. X-ray photoelectron spectroscopy verifies the expected stoichiometry, reveals mixed Mn 2+ /Mn 3+ and Co 2+ /Co 3+ valence states, and identifies oxygen vacancies – key features enabling simultaneous ionic and electronic conduction. Electrochemical impedance spectroscopy from 300 to 700 °C displays a rise in bulk conductivity, reaching ∼2.74 × 10 –2 S cm –1 at 700 °C. The activation energy deduced from Arrhenius plot analysis is ∼0.80 eV, an intermediate value between pure oxide-ion transport (>1 eV) and small-polaron hopping (0.1–0.6 eV), confirming mixed ionic–electronic conduction. AC conductivity follows Jonscher’s universal power law, and the temperature dependence of the frequency exponent “s” supports a correlated-barrier-hopping mechanism. These structural, microstructural, and transport characteristics establish BMCO as a promising candidate for various electrochemical applications like IT-SOFC electrodes, oxygen separation membranes, and electrochemical sensors.