Performance tuning of BaFeO3-based electrodes through nickel substitution for protonic ceramic cell applications

Abstract

The development of cobalt-free mixed ionic-electronic conductors (MIECs) for protonic ceramic fuel cells and electrolysis cells (PCFCs/PCECs) requires electrode materials that combine high electrochemical activity with chemical compatibility towards barium-based proton-conducting electrolytes. While many studies have focused on avoiding barium-containing electrode systems due to stability concerns, such materials are in fact highly attractive for PCFCs and PCECs because they share the same cation sublattice as BaCeO3- and BaZrO3-based electrolytes that might minimize interfacial reactions and secondary phase formation. In this context, the perovskite ferrite Pr0.6Ba0.4FeO3–δ represents a promising matrix for electrode design. The present work investigates the effect of partial iron substitution by nickel in Pr0.6Ba0.4Fe1–xNixO3–δ (x = 0.1, 0.2, 0.3) on structural properties, electrical transport behavior, and electrochemical performance. The materials were characterized by X-ray diffraction, four-probe DC conductivity measurements, and electrochemical impedance spectroscopy on symmetrical cells with BaCe0.5Zr0.3Y0.1Yb0.1O3–δ electrolyte. The results establish clear composition–structure–property correlations: the nickel content systematically affects the lattice parameters, governs the conductivity behavior in oxidizing and reducing atmospheres, and influences the electrode polarization resistance and depends strongly on the operating conditions. Notably, the optimal nickel concentration differs between oxidizing and reducing environments, which has direct implications for selecting electrode compositions for specific applications. The findings demonstrate that nickel-doped Pr0.6Ba0.4FeO3–δ offers a flexible compositional platform for designing cobalt-free, barium-containing MIEC electrodes with enhanced compatibility and performance in protonic ceramic electrochemical devices.