Operando Raman Investigation of Interfacial Molecular Vibrations for CO2 Electroreduction on Cu-Based Gas Diffusion Electrodes under Back Pressure

Abstract Back-pressure regulation serves as a promising strategy to boost electrochemical CO2 reduction performance, owing to its unique capability to enrich interfacial reactants and modulate reaction pathways. Nevertheless, dynamic tracking of gas-liquid-solid interfacial species evolution under practical milliampere-level reaction conditions remains largely underexplored. Herein, a customized flow-cell-coupled Raman platform was adopted to dynamically monitor the electrocatalytic CO2 conversion behavior of Cu-based electrodes, alongside the structural evolution of surface-adsorbed intermediates and interfacial hydrogen bond networks across a continuous back-pressure gradient (0−150 mbar). In the current density range of 0−100 mA·cm−2, elevating back pressure dramatically suppressed the hydrogen evolution reaction, with H2 selectivity dropping from 43.6% (0 mbar) to 16.7% (150 mbar). By contrast, the faradaic selectivity of C2+ products increased steadily from 19.6% to 59.3%, and the yield of oxygenated products was also positively correlated with back-pressure intensity. Operando Raman characterizations reveal that applied back pressure delivers dual interfacial modulation effects: it elevates the surface coverage of key CO reaction intermediates and reorganizes local hydrogen bond configurations. The optimized interfacial structure accumulates strongly hydrogen-bonded water molecules, which constrain the migration of protons and hydroxyl ions. Such structural regulation strengthens interfacial alkalinity and ultimately facilitates the electrocatalytic generation of C2+ products.