Probing the Active Surface Sites for CO Reduction on Oxide-Derived Copper Electrocatalysts

TLDR

CO electroreduction on oxide‑derived Cu correlates with metastable surface features that bind CO strongly. The study aims to identify strong CO‑binding sites supported by grain boundaries as the active sites for CO reduction on OD‑Cu, a first step toward understanding the surface chemistry needed for efficient CO electroreduction. Temperature‑programmed desorption of CO on OD‑Cu revealed distinct strong CO‑binding sites, different from terraces and stepped sites on polycrystalline Cu, supporting the hypothesis that grain‑boundary‑supported sites are active. H₂‑reduced OD‑Cu electrodes convert CO to acetate and ethanol with ~50 % Faradaic efficiency at moderate overpotential, but annealing at 350 °C reduces the surface‑area‑corrected current density 44‑fold and FE to <5 % due to loss of strong CO‑binding sites.

Abstract

CO electroreduction activity on oxide-derived Cu (OD-Cu) was found to correlate with metastable surface features that bind CO strongly. OD-Cu electrodes prepared by H-2 reduction of Cu2O precursors reduce CO to acetate and ethanol with nearly 50% Faradaic efficiency at moderate overpotential. Temperature-programmed desorption of CO on OD-Cu revealed the presence of surface sites with strong CO binding that are distinct from the terraces and stepped sites found on polycrystalline Cu foil. After annealing at 350 degrees C, the surface-area corrected current density for CO reduction is 44-fold lower and the Faradaic efficiency is less than 5%. These changes are accompanied by a reduction in the proportion of strong CO binding sites. We propose that the active sites for CO reduction on OD-Cu surfaces are strong CO binding sites that are supported by grain boundaries. Uncovering these sites is a first step toward understanding the surface chemistry necessary for efficient CO electroreduction.