Recent progress of in situ/operando characterization techniques for electrocatalytic energy conversion reaction

Catalysts can significantly promote the reaction dynamics and are therefore considered crucial components for achieving high electrochemical energy conversion efficiency. However, the active sites of the catalysts, particularly for nano-level and atomic-level catalysts commonly undergo reconstruction under practical applications. Therefore, obtaining an in-depth and systematic understanding on the real active sites through in situ/operando characterization techniques is a prerequisite for establishing the structureperformance relationship and guiding the future design of more efficient electrocatalysts. Herein, we summarize the recent progress of in situ/operando characterization techniques for identifying the nature of active sites of electrocatalysts when used in electrocatalytic energy conversion reaction. Specifically, our focus lies in the fundamental principles of various in situ/operando characterization techniques, with particular emphasis on their applications for electrocatalytic reactions. Beyond that, the challenges and perspective insights are also added in the final section to highlight the future direction of this important field.