Understanding of critical materials for reversible solid oxide cells through in-situ and operando characterization techniques

Reversible solid oxide cells (RSOCs) offer a highly efficient pathway for clean energy conversion and storage by switching between power generation and fuel synthesis modes. However, their widespread commercialization is fundamentally hindered by sluggish electrochemical reaction kinetics, performance degradation, and insufficient long-term durability under harsh operating conditions. Conventional ex-situ characterization fails to capture the dynamic structural and chemical evolution of critical materials during operation, obscuring the underlying mechanisms of performance decay. This review summarizes fundamental principles of advanced in-situ / operando methodologies and their applications in unravelling dynamic changes of RSOC materials, covering morphology evolution, crystal-phase transformation, metal valence variation, local coordination environment modulation, as well as identification of active sites and reaction mechanisms. The integration between experimental observations and theoretical calculations for uncovering atomic-scale mechanisms is highlighted. Current technical bottlenecks are analyzed, and targeted perspectives are proposed, aiming to provide strategic guidance for constructing advanced characterization workflows and developing high-performance, robust RSOC materials.