Advances in reversible protonic ceramic electrochemical cells operated below 723 K: theoretical insights and experimental developments

Lowering the operating temperature of ceramic electrochemical cells below 723 K can efficiently mitigate component degradation and reduce system costs. Compared with traditional oxygen-ion conducting ceramic electrochemical cells, reversible protonic ceramic electrochemical cells (R-PCECs) offer greater potential for operation below 723 K due to the low activation energy for proton conduction, thus attracting significant research attention over the past decade. However, maintaining reasonable performance and efficiency at reduced temperatures remains a critical challenge. This review provides a comprehensive summary of theoretical insights and recent experimental advancements in R-PCECs operated below 723 K. In the theoretical aspect, one-dimensional charge transportation models, the kinetics/polarization of electrodes, and two/three-dimensional multi-physics models are summarized, with a critical evaluation of existing models and their simulation results, especially for faradaic efficiency. Experimentally, efficient strategies for enhancing electrolyte, oxygen electrode, and fuel electrode performance are systematically reviewed and critically analyzed. Additionally, the potential of advanced computational approaches, such as high-throughput computation and machine learning-assisted methods, is discussed. Based on the comprehensive and critical discussion, detailed issues in the development of R-PCECs operated below 723 K are identified, and prospective research is outlined.