<i>In Situ</i> Infrared Spectroscopic Evidence of Enhanced Electrochemical CO₂ Reduction and C–C Coupling on Oxide-Derived Copper

Abstract

The reaction mechanism of CO₂ electroreduction 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 <i>in situ</i> surface-enhanced infrared absorption spectroscopy (SEIRAS) on metallic and mildly anodized copper thin films. The <i>in situ</i> SEIRAS results show that the preoxidation process can significantly improve the overall CO₂ reduction activity by (1) enhancing CO₂ activation, (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 CO₂ adsorption and activation. The rapid uptake of adsorbed *CO_atop also 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 C₂ product 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 CO₂ reduction.