Operando studies reveal active Cu nanograins for CO₂ electroreduction

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Carbon dioxide electroreduction is crucial for sustainable fuel and chemical synthesis.
• Copper (Cu) catalysts are effective for converting CO2 to multicarbon products (C2+), but active sites remain unclear.
• Understanding Cu nanocatalyst active sites requires advanced operando techniques.

Purpose of the Study:

• To comprehensively investigate the structural dynamics and active sites of Cu nanocatalysts during their lifecycle.
• To correlate catalyst structure with activity for CO2 electroreduction to C2+ products.
• To elucidate the role of metallic Cu nanograins and their boundaries in C-C coupling.

Main Methods:

• Operando analytical and four-dimensional electrochemical liquid-cell scanning transmission electron microscopy (4D-EC-LC-STEM).
• High-energy-resolution time-resolved X-ray spectroscopy (HER-TRXRS).
• Quantitative structure-activity correlation analysis.

Main Results:

• Cu nanoparticle ensembles transform into metallic Cu nanograins during electrolysis, then oxidize to Cu2O post-electrolysis.
• Metallic Cu nanograins, especially at grain boundaries, are identified as active sites for CO2 reduction under operating conditions.
• Higher fractions of metallic Cu nanograins correlate with significantly increased C2+ selectivity, with 7nm Cu showing sixfold higher selectivity than 18nm Cu.

Conclusions:

• Metallic Cu nanograins, rich in grain boundaries, provide undercoordinated active sites essential for C-C coupling in CO2 electroreduction.
• Nanocatalyst structural evolution under electrochemical conditions directly impacts catalytic performance.
• Multimodal operando techniques offer a powerful platform for understanding nanocatalyst behavior and optimizing performance.