UC Berkeley

In situ/operando liquid cell transmission electron microscopy (TEM) enables real-time visualization of physical and chemical processes in liquid environments at nanoscale resolution. It creates opportunities to understand the dynamic behavior of nanomaterials across various applications ranging from materials synthesis to energy storage, and chemical production. However, challenges remain in probing dynamic processes of nanomaterials under complex working conditions (e.g., electrocatalysis), which limits mechanistic understanding of the structure-performance correlations. The development of liquid cell TEM platform with enhanced spatial resolution and versatile functionalities, e.g., by implementing multimodal in situ/operando capabilities, is essential to overcome the challenge entailing the broader applications.This dissertation aims to deepen the fundamental understanding of dynamic processes of nanomaterials and reveal their structure-performance correlations by developing and applying in situ/operando liquid cell TEM. I focus on two topics of studies on electrocatalysts and nanomotors. The work begins by the innovations of liquid cell microdevices that address challenges in investigating electrochemical systems. By applying operando electron microscopy and X-ray spectroscopy, my systematic investigation uncovers the dynamic structural reconstruction of CuO nanowire-derived Cu under carbon dioxide reduction reaction (CO2RR) working conditions. Additionally, I discover the underlying mechanisms in nanomotor movement through in situ liquid cell TEM, thus providing new insights into the structure-performance relationships. In Chapter 1, I briefly introduce the fundamentals of in situ/operando liquid cell TEM and review its applications, including nucleation and growth of nanoparticles, the structural evolutions of electrocatalysts, and electrochemical processes at electrode-electrolyte interfaces of batteries. In Chapter 2, I provide an overview of typical liquid cell designs, followed by the latest techniques and optimized strategies for improving spatial resolution and extending functionality of liquid cells. I emphasize the newly developed polymer membrane-based electrochemical liquid cells, which have enabled high-resolution imaging as well as chemical analysis capabilities during electrochemical reactions. In Chapter 3, I combine the operando electrochemical liquid cell TEM (EC-TEM) with time-resolved X-ray absorption spectroscopy (XAS) to unveil the formation pathways of oxide-derived Cu (OD-Cu) active sites from CuO bicrystal nanowire precatalysts, driven by nanocrack generation and propagation. It provides new mechanistic insights into better control of catalyst structure and performance. In Chapter 4, I further investigate the temperature-dependent structural diversity of Cu nanoparticles formed during electrodeposition for electrocatalyst synthesis. In Chapter 5, I demonstrate the mechanism of the directional movement of CdCl₂·4H₂O nanomotors. The facet-dependent reactivity of nanomotor leads to ionic self-diffusiophoresis and drives its movement. Finally, in Chapter 6, I summarize the key findings of this dissertation and provide my perspectives on the future directions for advancing in situ/operando liquid cell TEM.