Three alkaline earths and two rare earths jointly enhance activity and stability of a high-entropy iron perovskite electrode for symmetrical solid oxide fuel cells

• A high-entropy iron perovskite electrode is designed for symmetrical fuel cells. • Alkaline/rare earth synergy enhances oxygen vacancies and stability of electrode. • The single-cell output performance increases by as high as 70 % at 850 °C. • The 150-hour long-term durability confirms its excellent redox durability. • A design pattern of efficient high-entropy iron perovskite electrode is done. Symmetrical solid oxide fuel cells (SSOFCs) have the great potential to be commercialized but remain a challenge of efficient electrode design. Here, we demonstrate that three alkaline earths and two rare earths metals jointly enhance the activity and stability of the iron perovskite electrode and discover a new efficient high-entropy iron-based perovskite electrode of Ce 0.2 La 0.2 Ba 0.2 Sr 0.2 Ca 0.2 FeO 3-δ (CLBSCF) for SSOFCs. The CLBSCF is synthesized via Pechini method and shows enhanced structural stability, conductivity, and catalytic activity, compared to state-of-the-art La 0.2 Sr 0.8 FeO 3-δ (LSF). Systematic characterization of symmetrical electrodes reveals the significant increase of oxygen vacancy and electrocatalytic activity of CLBSCF. CLBSCF electrode based half-cells electrode exhibit the lower polarization resistance of 0.065 Ω cm 2 in air and 0.36 Ω cm 2 in H 2 than that with LSF electrode (0.12 Ω cm 2 in air and 1.57 Ω cm 2 in H 2 ) at 850 °C. The single cell with CLBSCF achieves a higher peak power density of 571 mW cm -2 than that with LSF electrode (336 mW cm -2 ) at 850 °C. Long-term durability of SSOFC with CLBSCF electrode confirms its excellent stability. This work provides a design pattern for efficient high-entropy iron-based perovskite electrodes of fuel cells.