Undercoordinated Active Sites on 4H Gold Nanostructures for CO₂ Reduction

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Artificial carbon recycling through carbon dioxide (CO2) electroreduction is crucial for sustainability.
• Electrocatalyst surface structure significantly influences CO2 electroreduction reaction (CO2RR) rate and product selectivity.
• Controlling nanostructure phase and morphology is key to developing efficient CO2RR electrocatalysts.

Purpose of the Study:

• To investigate 4H gold (Au) nanostructures as advanced electrocatalysts for CO2 electroreduction.
• To compare the performance of 4H-phase Au nanoribbons, 4H/fcc-phase Au nanorods, and fcc-phase Au nanorods.
• To elucidate the structure-performance relationship in Au nanostructures for CO2-to-CO conversion.

Main Methods:

• Synthesis and characterization of Au nanostructures with controlled phase (4H, fcc) and shape (nanoribbons, nanorods).
• Electrochemical evaluation of CO2 electroreduction activity and selectivity using techniques like cyclic voltammetry and CO2 electrolysis.
• Surface structure elucidation via electrochemical probing and cluster expansion simulations, supported by density functional theory (DFT) calculations.

Main Results:

• A clear trend in CO production activity and selectivity was observed: 4H-nanoribbons > 4H/fcc-nanorods > fcc-nanorods.
• 4H Au nanoribbons achieved over 90% Faradaic efficiency for CO production, demonstrating high selectivity.
• The study identified undercoordinated sites, resulting from the combination of crystal phase and shape control, as highly reactive active sites.

Conclusions:

• 4H Au nanostructures, particularly nanoribbons, are highly effective electrocatalysts for selective CO2 to CO conversion.
• Controlling both crystal phase and morphology of Au nanocrystals is critical for optimizing CO2 electroreduction performance.
• The preferential exposure and high reactivity of undercoordinated sites in 4H Au nanostructures drive their enhanced catalytic activity.