Probing Activation and Deactivation Mechanisms in Electrochemical CO₂ Reduction Reaction and Water Splitting through In‐Situ/Operando Analysis

Abstract The transition to a carbon‐neutral society demands the development of efficient and durable electrocatalysts to drive electrochemical water splitting and CO 2 reduction reactions (CO 2 RR). To fabricate high‐performing electrocatalysts, it is essential to unveil catalyst materials’ activation and deactivation mechanisms under actual reaction conditions, a challenge that ex‐situ/post‐mortem characterization cannot fulfill. In‐situ transmission electron microscopy, X‐ray spectroscopy, and Raman spectroscopy, along with various other analytical techniques, are essential methods for revealing the structural and chemical properties of electrochemical catalyst materials in both bulk and surface. In‐situ/operando characterization offers unprecedented insights into the structural and electronic changes on catalyst surfaces, revealing critical aspects of catalytic activity, selectivity and stability during operation. These methods are useful in identifying active sites, understanding morphology and phase transitions, and uncovering the underlying mechanisms driving catalytic processes. This perspective explores recent works on the application of in‐situ/operando spectroscopic and microscopic techniques to electrochemical CO 2 RR and water splitting. By organizing recent findings, we highlight the irreplaceable role of in‐situ/operando analysis in refining catalyst design for enhanced performance and robustness. Furthermore, we discuss future directions for integrating these characterization methods into catalyst development workflows, offering a roadmap toward developing electrocatalyst materials for green hydrogen production and CO 2 reduction.