Dynamic Evolution from Single-Atom Catalysts to Active Nanograins for CO₂ Reduction.

Area of Science:

• Catalysis
• Materials Science
• Electrochemistry

Background:

• Tracking dynamic catalyst evolution at the nanoscale, especially for copper single-atom catalysts (Cu-SACs), is challenging due to rapid changes and reoxidation.
• Existing ex situ/in situ methods indirectly suggest structural reconstruction, but direct, time-resolved operando observations are needed.

Purpose of the Study:

• To provide direct experimental evidence of the dynamic evolution of Cu-SACs into copper nanostructures.
• To correlate catalyst structural evolution with performance in CO2 reduction reactions (CO2RR).

Main Methods:

• Utilized operando synchrotron-based high-energy-resolution X-ray spectroscopy and IR absorption spectroscopy to monitor structural and molecular changes.
• Employed operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM) for real-time imaging of atomic evolution.
• Applied operando electrochemical four-dimensional (4D) STEM to characterize the resulting nanostructures.

Main Results:

• Observed direct dynamic evolution from Cu-SACs to copper nanostructures rich in active nanograins.
• Cu-SACs supported on nanocarbon (Cu-SAC-NC) showed a 5-fold increase in multicarbon Faradaic efficiency (C2+ FE) due to enhanced metallic nanograin formation.
• Identified dense copper carbonyl (Cu-CO) intermediates and polycrystalline nanostructures with active grain boundaries as key features.

Conclusions:

• Nanocarbon support enhances conductivity, facilitating the formation of active metallic Cu nanograins and improving C2+ selectivity in CO2RR.
• Operando techniques provide direct insights into the dynamic structural evolution of catalysts under reaction conditions.
• Catalyst design should consider operando active structures, not just pristine ones, for optimized performance.