We investigated the catalytic activity and C2 selectivity in electrochemical carbon dioxide reduction reaction (CO₂RR) on two distinguished electrodeposited Cu oxides with distinct morphologies and structures. The electrode with a compact structure exhibited two times higher faradaic efficiencies of C2 products (40%). Through utilizing electrochemical surface-enhanced Raman spectroscopy (SERS), it was realized that the formation of a metastable phase (malachite) on electrode surfaces by consumption of ${\text{HCO}}_{\text{3}}^{-}$ could cause a shift in local pH. The analysis of SERS indicated a strong correlation between the presence of the malachite phase and strongly-adsorbed CO on electrode surfaces, preventing dimerization and further reduction. This malachite phase terminating the surface can hinder the charge exchange and interfere with further reductions in C2 products.