(Invited) Liquid Phase TEM for Studying Catalysis and Electrochemistry of Nanomaterials

Abstract

For the past few decades, nanomaterials of various sizes, shapes, and compositions have been synthesized and utilized in many different applications in heterogeneous catalysts and energy conversion systems. However, due to a lack of analytical tools that can characterize structural changes at the nanoscale level, many of their growth, transformations, and reactions are limitedly understood. The recent development of liquid‐phase transmission electron microscopy (TEM) is gaining attention as a new tool to directly observe chemical reactions that occur in solution. Due to its high spatial and temporal resolution, this technique is widely employed to reveal fundamental mechanisms relevant to nanomaterial chemistry. Here, the technical developments for liquid‐phase TEM are introduced. In addition, its use in in-situ liquid phase studies of the growth mechanism, 3D structures, surface reactions of heterogeneous catalytic nanoparticles will be discussed. Our in-situ observations with liquid phase TEM elucidate different types of non-classical pathway, including two-step nucleation, amorphous-to-crystalline transition, and coalescence of clusters, are involved in different conditions of catalytic nanoparticle formation. We also observe the diffraction patterns from individual heterogeneous catalytic nanoparticles as they rotate in the liquid cell, and ultimately, we are able to align and invert those images to obtain the 3D atomic structure of individual catalytic particles freely moving in liquid. Obtained 3D density maps unveil internal and surface structural features of those particles that have been either underestimated or unattainable in conventional analysis. Liquid phase TEM is further advanced to have a capability of resolving solution phase reactions of nanomaterials under in-situ electrical biasing conditions. Examples of in-situ biasing liquid TEM studies of electrochemical reactions in Li-air battery system will be also presented.