What can Raman spectroscopy really say about the adsorbed CO on roughened Cu electrodes in CO₂ electroreduction conditions?

RR conditions. Then, we use these structures to investigate how different surface roughness, facets, and CO adsorption sites influence the Raman spectra, and the intensity ratio of interest. We show that the changes in the Raman intensity ratio are not solely determined by CO coverage. The adsorption site has a significant influence on the spectral signature, while the realistic reconstruction of the Cu surface impacts the available sites in a potential-dependent manner. The local environment of the adsorbed CO, including the site, coverage, and secondary coordination sphere, affect the stretching and rotation mode frequencies and intensities. We conclude that the SERS signature, while it can be exceptionally useful, alone is insufficient to establish a rigorous, quantitative correlation between the surface coverage or density of species and the production rates of target products required for a clear structure-activity relationship.