Abstract Designing efficient electrocatalysts requires a detailed understanding of their structural evolution and active sites under operating conditions. In situ liquid‐phase transmission electron microscopy (LPTEM) enables observation of materials dynamics under realistic working environments with high spatial and temporal resolution. Over the past decades, LPTEM has progressed significantly from offering limited morphological information to now achieving atomic resolution. Moreover, it can be integrated with various external stimuli such as biasing, heating, and light sources, allowing for in situ observations under complex reaction conditions. In this review, the technical development of in situ liquid cells is first outlined, and key challenges faced in liquid‐phase electrochemical experiments are addressed. Major application areas and recent advances in the field of electrocatalysis are then summarized. In addition, the importance of emerging electron microscopy techniques that enhance in situ capabilities, such as 4D scanning transmission electron microscopy, is highlighted. Finally, practical experimental suggestions to improve the success rate of in situ studies, and put forward the potential future directions for the development of LPTEM in electrocatalysis are outlined. This review provides a comprehensive overview of in situ LPTEM study in electrochemistry from both technical and application perspectives, offering valuable guidance for researchers in this field.
Li et al. (Mon,) studied this question.