Advances and opportunities in in-situ/operando transmission electron microscopy

In situ and operando transmission electron microscopy (TEM) has become a powerful approach for probing structure–property relationships under realistic environments. This review summarizes recent advances in environmental TEM, emphasizing liquid-, gas-, and emerging plasma-phase platforms that enable direct observation of dynamic materials processes. In liquid-cell TEM, developments in multi-nanochannel MEMS, electrochemical architectures, and polymer- and ionic-liquid-based systems have expanded capabilities for studying electrochemical reactions, phase transformations, and interfacial phenomena. Gas-cell TEM advances—including ultrahigh-pressure operation, ultrathin back-supported SiNx membranes, graphene-based windows, and laser-integrated platforms—have significantly improved imaging fidelity and enabled operando studies of catalysis and surface reactions. The emergence of plasma-phase TEM introduces new opportunities to probe non-equilibrium plasma–materials interactions. In parallel, integration of advanced characterization and data-analysis approaches, such as 3D reconstruction, 4D-STEM, and artificial intelligence–assisted workflows, is accelerating quantitative operando materials characterization and expanding the scope of in situ electron microscopy.