In-Situ/Operando Raman Spectroscopy Techniques for In-Depth Decoupling CO2 Reduction Reaction Mechanisms

Electrocatalytic carbon dioxide reduction reaction (eCO2RR) is a pivotal negative carbon technology that converts greenhouse gas CO2 into value-added chemicals using renewable energy. However, its selectivity and efficiency are still limited by an incomplete understanding of active-phase dynamics, key intermediate formation, and reaction-pathway identification. Due to its molecular-level structural sensitivity and real-time monitoring capability, in-situ Raman spectroscopy has become a powerful tool for decoupling eCO2RR mechanisms by providing surface/interface-specific molecular fingerprints. This minireview systematically classifies and summarizes recent advances of in-situ Raman techniques applied to eCO2RR, emphasizing the enhancement principles and design strategies of each technique. The discussed approaches include surface-enhanced Raman spectroscopy, shell-isolated nanoparticle-enhanced Raman spectroscopy, nanoconfinement-enhanced Raman spectroscopy, membrane electrode assembly-based Raman spectroscopy, and sub-second time-resolved surface-enhanced Raman spectroscopy. Representative examples highlight how these techniques decouple complex mechanisms, from active-phase evolution to intermediate identification and pathway elucidation. Furthermore, we provided a mechanism map linking Raman-observable intermediates to elementary reaction steps, highlighted recent innovations in Raman cell design, and discussed future directions toward multimodal integration and quantitative analysis. This focused and critical perspective provides a practical roadmap for researchers aiming to apply in-situ Raman spectroscopy in complex electrocatalytic systems.