In Situ Surface-Enhanced Raman Spectroscopic Evidence on the Origin of Selectivity in CO₂ Electrocatalytic Reduction

The electrocatalytic reduction of CO₂ (CO₂ER) to liquid fuels is important for solving fossil fuel depletion. However, insufficient insight into the reaction mechanisms renders a lack of effective regulation of liquid product selectivity. Here, in situ surface-enhanced Raman spectroscopy (SERS) empowered by ¹³C/¹²C isotope exchange is applied to probing the CO₂ER process on nanoporous silver (np-Ag). Direct spectroscopic evidence of the preliminary intermediates, *COOH and *OCO^-, indicates that CO₂ is coordinated to the catalyst via diverse adsorption modes. Further, the relative Raman intensities of the above intermediates vary notably on np-Ag modified by Cu or Pd, and the liquid product selectivity also changes accordingly. Combined with density functional theory calculations, this study demonstrates that the CO₂ adsorption configuration is a critical factor governing the reaction selectivity. Meanwhile, *COOH and *OCO^- are key targets in the initial stage regulating liquid product selectivity, which could facilitate future selective catalyst design.