Graphene-Based Liquid Cell Designs for In Situ Liquid-Phase Transmission Electron Microscopy: Recent Developments and Perspectives.

Recent advances in liquid-phase transmission electron microscopy (TEM) have enabled the direct visualization of reaction pathways of nanomaterials, providing critical insights into diverse nanoscale processes such as crystallization, phase transition, shape transformation, etching, and nanoparticle motions. Among various liquid cells, graphene liquid cells (GLCs) are particularly advantageous due to the intrinsic properties of graphene-high electrical and thermal conductivity, exceptional mechanical flexibility, and radical scavenging effects-which allow atomic-scale spatial resolution and enhanced imaging stability. This review article highlights the recent progress in GLC-based liquid-phase TEM, focusing on the evolution of structural designs, including veil-type, well-type, liquid-flowing-type, and mixing-type GLCs. Each configuration offers unique advantages tailored to observing distinct types of nanoscale dynamic processes. These studies have elucidated both classical reaction pathways and complex, nonclassical mechanisms involving transient intermediates. Overall, this review highlights how developments in GLC designs have significantly advanced the capabilities of in situ liquid-phase TEM, providing unprecedented opportunities to study nanoscale processes at atomic resolution.