The water‐splitting reaction, including the hydrogen and oxygen evolution reactions, as well as the electrochemical oxygen and CO₂ reduction reactions offer promising solutions to address the global energy scarcity and the associated environmental issues. However, the lack of deep insight into the reaction mechanisms and clear identification of the catalytic active sites hinder any breakthrough for the development of efficient electrocatalysts with high performance and durability. Operando characterization techniques allowing in situ monitoring the surface oxidation state and local atomic‐structure transformation are capable of probing the active sites and promoting the fundamental understanding of the reaction mechanism in these systems. Herein, the recent applications of various operando characterization techniques in identifying the active sites and capturing the geometric structure, oxidation state, and local atomic‐structure evolution of the catalysts during water electrolysis and O₂/CO₂ electroreduction are thoroughly summarized. The challenges and outlook in developing operando techniques to further extend the understanding of the underlying mechanism during electrochemical energy‐conversion reactions are discussed.

中文翻译：

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原位/ Operando表征技术探讨电化学反应的能量转化

水分解反应，包括氢气和氧气的放出反应，以及电化学的氧气和CO ₂还原反应为解决全球能源短缺和相关的环境问题提供了有希望的解决方案。然而，缺乏对反应机理的深入了解和对催化活性位点的清楚识别阻碍了开发具有高性能和耐久性的高效电催化剂的任何突破。可以原位监测表面氧化态和局部原子结构转变的Operando表征技术能够探测活性位点，并促进对这些系统中反应机理的基本理解。在此，各种操作表征技术在识别活性位点和捕获几何结构，氧化态，_对2 / CO _2的电还原进行了全面总结。讨论了开发操作技术以进一步扩展对电化学​​能量转换反应过程中潜在机理的理解的挑战和前景。