Direct formation of copper nanoparticles from atoms at graphitic step edges lowers overpotential and improves selectivity of electrocatalytic CO₂ reduction

A key strategy for minimizing our reliance on precious metals is to increase the fraction of surface atoms and improve the metal-support interface. In this work, we employ a solvent/ligand/counterion-free method to deposit copper in the atomic form directly onto a nanotextured surface of graphitized carbon nanofibers (GNFs). Our results demonstrate that under these conditions, copper atoms coalesce into nanoparticles securely anchored to the graphitic step edges, limiting their growth to 2-5 nm. The resultant hybrid Cu/GNF material displays high selectivity in the CO₂ reduction reaction (CO₂RR) for formate production with a faradaic efficiency of ~94% at -0.38 V vs RHE and a high turnover frequency of 2.78 × 10⁶ h^-1. The Cu nanoparticles adhered to the graphitic step edges significantly enhance electron transfer to CO₂. Long-term CO₂RR tests coupled with atomic-scale elucidation of changes in Cu/GNF reveal nanoparticles coarsening, and a simultaneous increase in the fraction of single Cu atoms. These changes in the catalyst structure make the onset of the CO₂ reduction potential more negative, leading to less formate production at -0.38 V vs RHE, correlating with a less efficient competition of CO₂ with H₂O for adsorption on single Cu atoms on the graphitic surfaces, revealed by density functional theory calculations.