Mechanistic Insights into Active Sites for Electrochemical CO2 and CO Reduction over the Strain-Engineered Dealloyed Cu
Nanoporous Cu produced by chemical dealloying is a promising catalyst for electrochemical CO2 reduction owing to its tunable chemistry, morphology, and surface defect sites. However, how dealloying controls the atomic-scale structure of Cu ligaments and how these features govern catalytic behavior remain unclear, particularly in nanostructured catalysts under realistic operating conditions. Here, we synthesize nanoporous Cu by dealloying Cu20Zn80 in H3PO4 at different temperatures, enabling control over ligament sizes from the nanoscale to the microscale. Nanoporous Cu outperforms polycrystalline Cu for CO reduction, with the sample dealloyed at 15 {\deg}C reaching 60% Faradaic efficiency at -0.65 V vs. RHE. Using in situ synchrotron X-ray diffraction and cryogenic atom probe tomography, we trace the structural and chemical evolution during dealloying, revealing, for the first time, the sequential phase transitions from epsilon brass to gamma brass to Cu and chemical segregation of Cu and Zn within nano-ligaments. We further establish a quantifiable strain metric linking surface defect density to ligament surface strain, quantified from the asymmetry of synchrotron XRD peaks. This approach reveals a direct correlation between catalytic activity and ligament surface strain, identifying surface strain as a practical descriptor for designing nanostructured Cu catalysts for CO2 reduction under realistic operating conditions.