Cerium‐Entropy Coupling Boosts Oxygen Vacancy Density and Bifunctional Oxygen Electrocatalysis in Reversible Protonic Ceramic Electrochemical Cells

Abstract Reversible protonic ceramic electrochemical cells (R‐PCECs) represent a promising frontier for next generation fuel cell technology. However, their widespread commercialization is hindered by the limited electrocatalytic activity of air electrode materials. To achieve outstanding structural stability and bifunctional oxygen electrocatalytic activity, herein, a novel A site high entropy perovskite doped with trace cerium, Ce 0.05 Pr 0.19 La 0.19 Ba 0.19 Sr 0.19 Ca 0.19 CoO 3‐δ (CPLBSCC) is reported. Cerium doping at 5 at% markedly increases the oxygen vacancy concentration and enhances the triple conduction capability. When employed as the air electrode in R‐PCECs, CPLBSCC achieves a peak power density of 2.06 W·cm −2 in fuel cell (FC) mode and a maximum current density of ‐3.56 A·cm −2 at 1.3 V in electrolysis cell (EC) mode at 700 °C. The cell also demonstrates excellent long term durability, sustaining stable operation for 240 hours in both FC and EC modes, and undergoing 12 reversible (120 h) FC–EC cycles with slight performance degradation. This work underscores the promise of combining high entropy A site design with trace cerium doping as an effective strategy for developing next generation air electrode materials in advanced electrochemical energy conversion systems.