Effect of Gold Catalyst Surface Morphology on Wetting Behavior and Electrochemical CO₂ Reduction Performance in a Large-Area Zero-Gap Gas Diffusion Electrolyzer

Abstract

Catalyst surface area and wetting behavior are key factors in determining the performance of gas diffusion electrode (GDE) electrolyzers for electrochemical CO 2 reduction. In this work, we report the integration of sub-1 μm thick nanoporous gold (npAu) catalyst coatings into a large-area (25 cm 2 ) zero-gap electrolyzer. The npAu coatings were prepared by magnetron sputtering (MS) of thin AgAu alloy films on the microporous carbon layer of a gas diffusion layer (GDL) followed by Ag leaching. Compared to MS Au films of the same thickness, npAu catalyst coatings enable higher Faradaic efficiencies and improved catalyst stability for CO 2 -to-CO reduction with Faradaic efficiencies of up to 88% at 100 mA/cm 2 . For a 800 nm npAu coating, the device level energy efficiency for CO 2 to CO conversion reaches 45% (52% for CO + H 2 ) at 100 mA/cm 2 with a single pass CO 2 conversion efficiency of ∼12%. Contact angle measurements reveal that npAu coatings provide a more hydrophobic electrode interface compared to MS Au coatings, suggesting that the more hydrophobic interfacial environment of npAu coatings helps mitigating electrode flooding which is associated with performance deterioration over time.

Insights into electrolyte flooding in flexible gas diffusion electrodes for CO2 electrolysis: from mechanisms to effective mitigation strategies

“…Managing flooding of liquid electrolytes into the porous structure remains a critical practical challenge for GDEs with operational stability in CO 2 electrolysers. 12,14,80–82…”

“…Managing ooding of liquid electrolytes into the porous structure remains a critical practical challenge for GDEs with operational stability in CO 2 electrolysers. 12,14,[80][81][82] To date, the ooding pitfall of the carbon-based GDE is mainly on account of three reasons: electrowetting, 83 uneven pressure distributions across the GDE, 84,85 and salt precipitation. 14 Electrowetting means that the liquid generally becomes easily spread over the solid surface under an applied electrical eld.…”