Evolution and Reconstruction of Air-Electrode Surface Composition in Reversible Protonic Ceramic Cells: Mechanisms, Impacts on Catalytic Performance, and Optimization Strategies - A Review.

Reversible protonic ceramic cells (R-PCCs) are at the forefront of electrochemical conversion devices, capable of reversibly and efficiently converting chemical energy into electricity at intermediate temperatures (350-700 °C) with zero carbon emissions. However, slow surface catalytic reactions at the air-electrode often hinder their performance and durability. The electrode surface is not merely an extension of the bulk structure, equilibrium reconstruction can lead to significantly different crystal-plane terminations and morphologies, which are influenced by material's intrinsic properties and external reaction conditions. Understanding electrode surface evolution at elevated temperatures in water-containing, oxidative atmospheres presents significant importance. In this review, a comprehensive summary of recent processes in applying advanced characterization techniques for high-temperature electrode surfaces is provided, exploring the correlations between surface evolution and performance fluctuations by examining the structural evolution and reconstruction of various air-electrode surfaces associated with degradation and activation phenomena, offering insights into their impact on electrode performance. Furthermore, reported strategies and recent advances in enhancing the electrochemical performance of R-PCCs through engineering air-electrode surfaces is discussed. This review offers valuable insights into surface evolution in R-PCCs and is expected to guide future developments in high-temperature catalysis, solid-state ionics, and energy materials.