Visualizing Electrochemical CO ₂ Reduction Reaction: Recent Progress of In Situ Liquid Cell Transmission Electron Microscopy

Abstract The electrochemical carbon dioxide reduction reaction (CO 2 RR), driven by renewable energy, represents a promising approach for converting CO 2 into valuable fuels and chemicals, addressing pressing energy and environmental challenges. However, the development of high‐performance CO 2 RR electrocatalysts remains constrained by a limited understanding of their dynamic evolution mechanisms, intrinsic stability factors, and activity origins under operational conditions. Transmission electron microscopy (TEM), with its unparalleled spatial resolution at the nanoscale and atomic level, combined with its microregional analytical capabilities, has become a vital tool for investigating heterogeneous electrocatalysis. Among these techniques, in situ liquid cell TEM (LC‐TEM) enables real‐time visualization of structural and morphological changes in catalysts during CO 2 RR. This review critically examines recent advancements in in situ LC‐TEM and its applications in CO 2 RR, focusing on three key aspects of electrocatalysts: the dynamic evolution of morphology, transformation of phase structure, and the identification of active sites. It highlights the pivotal role of in situ LC‐TEM in elucidating structure–activity relationships and the activation and deactivation mechanisms of electrocatalysts. Moreover, the review discusses the primary challenges facing in situ LC‐TEM and outlines future directions for advancing its applications in CO 2 electrolysis research.