The reaction mechanism of CO2electroreduction on oxide-derived copper has not yet been unraveled even though high C2+Faradaic efficiencies are commonly observed on these surfaces. In this study, we aim to explore the effects of copper anodization on the adsorption of various CO2RR intermediates using in situsurface-enhanced infrared absorption spectroscopy (SEIRAS) on metallic and mildly anodized copper thin films. The in situSEIRAS results show that the preoxidation process can significantly improve the overall CO2reduction activity by (1) enhancing CO2activation, (2) increasing CO uptake, and (3) promoting C–C coupling. First, the strong *COO–redshift indicates that the preoxidation process significantly enhances the first elementary step of CO2adsorption and activation. The rapid uptake of adsorbed *COatopalso illustrates how a high *CO coverage can be achieved in oxide-derived copper electrocatalysts. Finally, for the first time, we observed the formation of the *COCHO dimer on the anodized copper thin film. Using DFT calculations, we show how the presence of subsurface oxygen within the Cu lattice can improve the thermodynamics of C2product formation via the coupling of adsorbed *CO and *CHO intermediates. This study advances our understanding of the role of surface and subsurface conditions in improving the catalytic reaction kinetics and product selectivity of CO2reduction.