Advanced Cobalt‐Free Perovskite Oxide‐Based Air Electrodes for Protonic Ceramic Electrolysis Cells

Protonic ceramic electrolysis cells (PCECs) are regarded as a promising technology for producing green hydrogen due to the lower operational temperatures, higher conversion efficiencies, enhanced durability/safety, no requirement of hydrogen drying system and simplified water management over the traditional oxygen‐ion‐conducting solid oxide electrolysis cells. Nevertheless, the overall performance of PCECs is hindered by the slow kinetics of oxygen evolution reaction (OER) and insufficient triple conductivities (H + /O 2− /e − ) of air electrodes (e.g., perovskite oxides) at lower temperatures. Although remarkable advancements have been achieved about the development of cobalt‐based perovskite air electrodes (highly active but instable), designing optimal and highly efficient/durable air electrodes for PCECs remains challenging. Herein, an in‐time and critical review about the advances in designing cobalt‐free air electrodes for PCECs is presented by highlighting the fundamental mechanisms, performance‐influencing factors, and the superiority of cobalt‐free perovskite oxides over cobalt‐based counterparts. Several distinct design strategies to boost the OER activity/durability and thermo‐mechanical compatibility of cobalt‐free air electrodes for PCECs are also proposed. Finally, current limitations/contradictions, existed challenges/controversies and future directions are presented. This review aims to provide critical insights for the rational design of high‐efficiency and long‐lasting air electrodes for PCECs to realize widespread applications.