Configurational Entropy-Driven Oxide-Ion Transport in Rare-Earth High-Entropy Fluorite Electrolytes for Low-Temperature Fuel Cells

Lowering the operating temperature of ceramic fuel cells requires electrolyte materials that maintain high oxide-ion conductivity while remaining structurally stable in the intermediate-temperature regime. In this study, a five-component rare-earth high-entropy fluorite oxide, Ce 0.20 Sm 0.20 La 0.20 Nd 0.20 Gd 0.20 O 2−δ (RE-HEOs), was synthesized and evaluated as a promising electrolyte for low-temperature ceramic fuel cells (CFCs). Lattice disorder and oxygen-defect related features were evaluated by Raman spectroscopy and XPS, while thermogravimetric analysis was used to assess oxygen-loss behavior. The electrochemical measurements were done by impedance spectroscopy and single-cell polarization/power testing. The prepared electrolyte exhibited a conductivity of 0.15 S cm –1, while delivering a peak power density (PPD) of 843 mW cm –2 at 550 °C. Compared with SDC under identical testing conditions, the high-entropy fluorite showed markedly enhanced oxide-ion conductivity and peak power density. Density functional theory calculations indicate that multication disorder alters the electronic structure of the fluorite lattice, shifting the O 2p-band center toward the Fermi level, which is consistent with an increased tendency for oxygen-vacancy formation and facilitated oxide-ion migration. The results establish rare-earth high-entropy fluorites as a scalable design strategy for enhancing electrolyte performance in low-temperature ceramic fuel cells.