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

Catalyst surface area and wetting behavior are key factors in determining the performance of gas diffusion electrode (GDE) electrolyzers for electrochemical CO2 reduction. In this work, we report the integration of sub-1 mu m thick nanoporous gold (npAu) catalyst coatings into a large-area (25 cm2) 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 CO2-to-CO reduction with Faradaic efficiencies of up to 88% at 100 mA/cm2. For a 800 nm npAu coating, the device level energy efficiency for CO2 to CO conversion reaches 45% (52% for CO + H2) at 100 mA/cm2 with a single pass CO2 conversion efficiency of similar to 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.