Mechanistic Insights for Low-Overpotential Electroreduction of CO₂ to CO on Copper Nanowires

Recent developments of copper (Cu)-based nanomaterials have enabled the electroreduction of CO₂ at low overpotentials. The mechanism of low-overpotential CO₂ reduction on these nanocatalysts, however, largely remains elusive. We report here a systematic investigation of CO₂ reduction on highly dense Cu nanowires, with the focus placed on understanding the surface structure effects on the formation of CO (∗ denotes an adsorption site on the catalyst surface) and the evolution of gas-phase CO product (CO(g)) at low overpotentials (more positive than -0.5 V). Cu nanowires of distinct nanocrystalline and surface structures are studied comparatively to build up the structure-property relationships, which are further interpreted by performing density functional theory (DFT) calculations of the reaction pathway on the various facets of Cu. A kinetic model reveals competition between CO(g) evolution and ∗CO poisoning depending on the electrode potential and surface structures. Open and metastable facets such as (110) and reconstructed (110) are found to be likely the active sites for the electroreduction of CO₂ to CO at the low overpotentials.