Insights into the Morphological Changes and Electrochemical Analysis of High Entropy Spinel Oxide under Wet Air

Developing high-performance air electrodes for proton conducting solid oxide electrolysis cells (SOECs) is crucial to enhancing the overall efficiency of the cell. The electrodes based on high entropy oxides with different cations ameliorate the durability and electrocatalytic activity over conventional air electrode materials due to the synergistic effects. This report deals with investigating spinel-based high entropy oxide (CuLiFeCoNi)_1.4Mn_1.6O₄ (CM-HE) as a promising air electrode material with 3% H₂O containing air as feed gas. CM-HE maintained its phase stability even after being treated in wet air at 700 °C. Micrographs of the as-sintered and wet air-annealed samples showcased the growth of catalytically active (111) octahedral planes. X-ray photoelectron spectroscopy results confirmed the presence of multivalent cations (Mn, Fe, Ni, Co, and Cu) and oxygen species (O^1–/2– and OH^–) that contributed to water oxidation reaction (WOR) and oxygen evolution reaction (OER). DC conductivity studies under operando conditions unraveled the enhanced conduction with excellent surface exchange (1.35 ×10^–3 cm² s^–1) and chemical diffusion (7.58 ×10^–3 cm² s^–1) coefficients for oxygen species. Impedance spectra of the CM-HE|BZY|CM-HE symmetric cells revealed a lower area-specific resistance (0.08 Ω cm²) and reduced polarization loss under wet air, which was attributed to enhanced WOR and OER on the electrode surface. These results exalt CM-HE as a robust SOEC air electrode candidate.