Mapping reaction pathways and catalyst dynamics in electrochemical CO₂ reduction through in situ and operando...

Electrochemical CO₂ reduction reaction (eCO₂RR) provides a promising route for converting CO₂ into fuels and chemical feedstocks using renewable electricity. However, the dynamic nature of catalyst surfaces under reaction conditions complicates the identification of active sites and reaction intermediates, posing a major challenge for the rational design of efficient catalysts. In situ and operando characterisation techniques have therefore emerged as essential tools for directly probing catalyst behaviour under working electrochemical conditions. In this review, we present a unified perspective that integrates spectroscopy and microscopy techniques to correlate reaction intermediates, catalyst electronic structure evolution, and catalyst restructuring during eCO₂RR. Spectroscopic approaches, including surface-enhanced Raman spectroscopy (SERS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray absorption spectroscopy (XAS), enable direct identification of key reaction intermediates and electronic structure changes during eCO₂RR. Complementarily, in situ microscopy techniques such as electrochemical atomic force microscopy (EC-AFM), electrochemical scanning tunnelling microscopy (EC-STM), and liquid-cell transmission electron microscopy (EC-TEM) reveal dynamic restructuring of the catalyst surface at the nanoscale and atomic scale. By bridging molecular-level intermediate identification with nanoscale structural evolution, this review highlights how dynamic catalyst behaviour governs activity and selectivity, providing new insight into the identification of true active phases. This integrated framework offers emerging strategies for rational catalyst design toward stable and selective CO₂ reduction catalysts.