Operando Spectroscopic Insights into CO₂ Reduction at Electrode/Polyelectrolyte Interfaces

The electrode/polyelectrolyte interface is a notable feature in modern electrochemical technologies that utilize membrane electrode assembly (MEA) configurations. However, its interfacial structure and catalytic behavior remain poorly understood. Here, we developed an integrated operando Raman spectroscopy and mass spectrometry (MS) method, to directly investigate the CO₂ reduction mechanism at the electrode/polyelectrolyte interface within a practical MEA electrolyzer operating at high current densities. Combined with isotope labeling experiments and ab initio molecular dynamics (AIMD) simulations, we provide, for the first time, the direct spectroscopic evidence of *CCO, a crucial intermediate for C₂ product formation, which has been frequently hypothesized but rarely detected in previous studies. By contrast, the linearly adsorbed *CO_L intermediate, typically observed in conventional liquid electrolytes, was absent. These distinct behaviors arise from the unique structure of the electrode/polyelectrolyte interface, which shifts the rate-determining step from the usual C-C coupling to the *CCO hydrogenation in the conversion of CO₂ to C₂ products. This study not only deepens our understanding of electrode/polyelectrolyte interfacial characteristics but also offers valuable insights for advancing the performance of CO₂ MEA electrolyzers.