Hydrophobic Surface Modification Enables Tandem Ag/Cu Catalysis for CO₂ Electroreduction

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Silver-copper (Ag-Cu) tandem catalysts show potential for enhanced C2+ formation in CO2 electroreduction.
• However, Ag/Cu catalysts fabricated via PVD/sputtering lack ionomers and exhibit pure copper-like behavior in flow cells, failing to show tandem enhancement.
• Surface hydrophobicity is crucial, as exposed Ag surfaces reduce hydrophobicity, hindering CO2 transport and tandem pathways.

Purpose of the Study:

• To investigate the effect of hydrophobic surface modification on Ag-Cu tandem catalysts for CO2 electroreduction.
• To address the limitations of CO2 transport and tandem pathway suppression in flow cells.
• To optimize Ag-Cu catalyst performance for C2+ product selectivity and partial current density.

Main Methods:

• Fabrication of well-defined layered Ag/Cu catalysts using PVD/sputtering.
• Hydrophobic surface modification using 1-dodecanethiol (DDT).
• Performance evaluation in flow cells, including contact-angle measurements, Faradaic efficiency, partial current density, and product selectivity (e.g., ethanol/ethylene ratio).
• In situ Raman spectroscopy to analyze reaction intermediates.

Main Results:

• The DDT-modified Ag/Cu catalyst (DDT-Ag/Cu) achieved a 74.09 ± 1.69% Faradaic efficiency for C2+ products.
• A high partial current density of 370.5 ± 8.45 mA cm-2 was recorded at 500 mA cm-2.
• DDT-Ag/Cu outperformed benchmark Cu and unmodified Ag/Cu catalysts by approximately 65%.
• Ethanol selectivity was enhanced, doubling the ethanol-to-ethylene ratio from ~0.5 to ~1.0.
• In situ Raman spectroscopy indicated distinct intermediates under hydrophobic conditions.

Conclusions:

• Hydrophobic surface modification using DDT is an effective strategy to enhance Ag-Cu tandem catalyst performance in CO2 electroreduction flow cells.
• Improved hydrophobicity facilitates CO2 transport to the catalyst surface, promoting tandem pathways.
• The study clarifies the intrinsic behavior of Ag-Cu tandem catalysis and offers a practical approach for boosting C2+ formation efficiency.