Atomic dynamics of electrified solid-liquid interfaces in liquid cell TEM

Electrified solid-liquid interfaces play a key role in various electrochemical processes relevant to electrocatalysis^1-3, batteries^4,5, and supercapacitors^6,7 in energy science, and other processes in biology⁸ and geochemistry⁹. The electron and mass transport at the electrified interfaces may result in structural modifications that remarkably influence the reaction pathways, for example, electrocatalyst surface restructuring during reactions can significantly impact the catalysis mechanisms and reaction products^1-3. Despite its significance, direct probing the atomic dynamics of solid-liquid interfaces under electric biasing is challenging due to the nature of being buried in liquid electrolytes and the limited spatial resolution of current techniques for in situ imaging through liquids. Here, with our development of advanced polymer electrochemical liquid cells for transmission electron microscopy, we are able to directly monitor the atomic dynamics of electrified solid-liquid interfaces during Cu-catalyzed CO₂ electroreduction reactions. Our observation reveals a fluctuating liquid-like amorphous interphase. It undergoes reversible crystalline-amorphous structural transformations and flows along the electrified Cu surface, thus mediating the crystalline Cu surface restructuring and mass loss through the interphase layer. The combination of real-time observation and theoretical calculations unveils an amorphization-mediated restructuring mechanism resulting from charge-activated surface reactions with the electrolyte. Our results hold significant implications for utilizing transient interphase to control catalyst surface restructuring, thus tuning the catalytic reactions. It also opens many opportunities to explore the atomic dynamics and its impact in broad systems involving electrified solid-liquid interfaces by taking advantage of the in situ imaging capability.