Mechanistic Insights into the Enhanced Activity and Stability of Agglomerated Cu Nanocrystals for the Electrochemical Reduction of Carbon Dioxide to <i>n</i>‑Propanol

The reduction of carbon dioxide (CO₂) to <i>n-</i>propanol (CH₃CH₂CH₂OH) using renewable electricity is a potentially sustainable route to the production of this valuable engine fuel. In this study, we report that agglomerates of ∼15 nm sized copper nanocrystals exhibited unprecedented catalytic activity for this electrochemical reaction in aqueous 0.1 M KHCO₃. The onset potential for the formation of <i>n-</i>propanol was 200–300 mV more positive than for an electropolished Cu surface or Cu⁰ nanoparticles. At −0.95 V (vs RHE), <i>n-</i>propanol was formed on the Cu nanocrystals with a high current density (<i>j</i>_{<i>n</i>‑propanol}) of −1.74 mA/cm², which is ∼25× larger than that found on Cu⁰ nanoparticles at the same applied potential. The Cu nanocrystals were also catalytically stable for at least 6 h, and only 14% deactivation was observed after 12 h of CO₂ reduction. Mechanistic studies suggest that <i>n-</i>propanol could be formed through the C–C coupling of carbon monoxide and ethylene precursors. The enhanced activity of the Cu nanocrystals toward <i>n-</i>propanol formation was correlated to their surface population of defect sites