The electrochemical reduction of carbon dioxide (CO₂R) offers a sustainable pathway for converting CO₂ into value-added chemicals and fuels, contributing to industrial decarbonization. However, achieving high selectivity and stability at industrially relevant current densities remains challenging, largely due to the complex and dynamic nature of the electrochemical interface. While copper-based catalysts can facilitate multi-carbon product formation via C–C coupling, the intricate interplay between catalyst surfaces, electrolyte ions, interfacial water networks, and surface-bound intermediates complicates mechanistic understanding and device optimization.

Recent studies increasingly recognize the role of interfacial water in governing reaction pathways by mediating proton transfer and stabilizing intermediates. Water’s ability to form complex hydrogen-bond networks creates local solvent structures that dynamically respond to changes in potential, current density, and ionic composition. In parallel, electrolyte ions and adsorbates further perturb water organization and local pH, modifying selectivity. Yet, most in situ studies are restricted to low current densities, limiting their relevance to practical CO₂R systems.

Here, we employed an integrated approach combining operando Raman spectroscopy in membrane-electrode assembly (MEA) type electrolyser and 2D- correlated Raman spectroscopy to investigate how interfacial environments evolve during CO₂R under high current densities (1A cm^-2). Our study reveals that the structure and orientation of interfacial water layers respond dynamically to applied potential, local ion concentrations, and surface-adsorbed species. These transformations play a central role in modulating proton availability, reaction intermediate stabilization, and overall product selectivity. We identify distinct regimes where changes in interfacial organization correlate with shifts in reaction pathways, influencing the balance between desired multi-carbon products and competing side reactions.

By directly capturing the evolving interfacial landscape under realistic operating conditions, our findings underscore the importance of water structuring as critical design parameters in CO₂R systems. This understanding extends beyond traditional catalyst optimization approaches, offering new levers to improve electrochemical performance through targeted control of interfacial dynamics.