In situ/Operando Investigation for Heterogeneous Electro-Catalysts: From Model Catalysts to State-of-the-Art Catalysts

Electrochemical reactions, including water splitting, oxygen reduction, hydrogen oxidation, carbon dioxide reduction, nitrogen oxide reduction, etc., are critical for sustainable energy conversion and storage. Achieving high efficiency in these reactions requires catalysts with superior activity, selectivity, and stability, often realized through nanostructured metal catalysts. However, practical challenges such as low selectivity and catalytic degradation persist. In situ and operando characterization techniques offer real-time insights into catalyst behavior under reaction conditions, enabling a deeper understanding of structure–performance relationships and, therefore, guiding the design and optimization of electro-catalysts. This review discusses the common in situ/operando techniques, highlights their applications in model catalysts, including single-atom and single-crystal catalysts, and further explores their combinational analysis to study practical complex nanocatalysts. Finally, we provide suggestions and perspectives on the development of the in situ/operando techniques to further advance the field of electrochemical catalysis.