Exploring hydration of air electrodes for protonic ceramic cells: A review

Protonic ceramic cells (PCCs) are promising candidates for efficient energy transformation and storage at intermediate temperatures. However, the sluggish kinetics of conventional air electrodes pose a significant bottleneck, limiting their performance. Hydration, by enhancing proton absorption and transport within air electrodes, extends the triple-phase boundary and improves reaction kinetics, making it a key factor in optimizing PCC performance. This review presents a comprehensive summary of the latest advancements in understanding and enhancing hydration in PCCs. Initially, the hydration mechanism and its critical role in PCCs are discussed. A detailed overview follows, covering various methodologies used to assess the hydration capacity of air electrodes, including advanced characterization techniques, electrochemical analysis methods, and theoretical calculations. Additionally, several effective strategies to enhance hydration capacity are elucidated. These strategies range from elemental doping and tuning of non-stoichiometric compositions to the development of heterogeneous structures and the emerging application of machine learning. Ultimately, the review highlights current challenges and outlines the potential for future breakthroughs in PCC technology.