An Efficient High‐Entropy Perovskite‐Type Air Electrode for Reversible Oxygen Reduction and Water Splitting in Protonic Ceramic Cells

Abstract Reversible protonic ceramic electrochemical cells (R‐PCECs) are emerging as ideal devices for highly efficient energy conversion (generating electricity) and storage (producing H 2 ) at intermediate temperatures (400–700 °C). However, their commercialization is largely hindered by the development of highly efficient air electrodes for oxygen reduction and water‐splitting reactions. Here, the findings in the design of a highly active and durable air electrode are reported: high‐entropy Pr 0.2 Ba 0.2 Sr 0.2 La 0.2 Ca 0.2 CoO 3− δ (HE‐PBSLCC), which exhibits impressive activity and stability for oxygen reduction and water‐splitting reactions, as confirmed by electrochemical characterizations and structural analysis. When used as an air electrode of R‐PCEC, the HE‐PBSLCC achieves encouraging performances in dual modes of fuel cells (FCs) and electrolysis cells (ECs) at 650 °C, demonstrating a maximum power density of 1.51 W cm −2 in FC mode, and a current density of −2.68 A cm −2 at 1.3 V in EC mode. Furthermore, the cells display good operational durabilities in FC and EC modes for over 270 and 500 h, respectively, and promising cycling durability for 70 h with reasonable Faradaic efficiencies. This study offers an effective strategy for the design of active and durable air electrodes for efficient oxygen reduction and water splitting.