Operando Electrochemical Liquid-Cell Scanning Transmission Electron Microscopy (EC-STEM) Studies of Evolving Cu Nanocatalysts for CO2 Electroreduction

The design and synthesis of nanocatalysts with well-defined sizes, compositions, and structures have revolutionized our accessibility to tunable catalyst activity and selectivity for a variety of energy-related electrochemical reactions. Nonetheless, establish-ing structure-(re)activity correlations requires the understanding of the dynamic evolution of pristine nanocatalysts and the identification of their active states under operating conditions. We previously communicated the operando observation of Cu nanocatalysts evolving into active metallic Cu nanograins for CO2 electroreduction (Yang et al. Nature 2023, 614, 262-269). Here, we expand our discussion to the technical capabilities and further research applications of operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM), which enables quantitative electrochemistry while tracking dynamic structural evolution of sub-10 nm Cu nanocatalysts. The coexistent H2 bubbles, often disruptive to operando spectroscopy, are an effective approach to create a thin-liquid layer that significantly improves spatial resolution while remaining electrochemically accessible to Cu nanocatalysts. Operando four-dimensional (4D) STEM in liquids provides insights into the complex structure of active polycrystalline metallic Cu nanograins. With continuous technical developments, we anticipate that operando EC-STEM will evolve into a powerful electroanalytical method to advance our understanding of a variety of nanoscale electrocatalysts at solid/liquid interfaces.

Automated summary

The design and synthesis of nanocatalysts with well-defined sizes, compositions, and structures have greatly enhanced our ability to control catalyst activity and selectivity for energy-related electrochemical reactions. By using operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM), the dynamic evolution of Cu nanocatalysts during CO2 electroreduction was observed, providing valuable insights into their active states. With further technical advancements, operando EC-STEM is expected to become a powerful electroanalytical method for studying nanoscale electrocatalysts at solid/liquid interfaces.