Highly Selective Electrochemical Bicarbonate Conversion across C ₁ and C ₂ Products by Interface-Modulation with a Stripping Compartment

Electrochemical reactive carbon capture (eRCC) is a promising route for carbon utilization, but its performance is limited by fundamental constraints in conventional membrane electrode assembly (MEA) configurations. The key steps of eRCC, such as CO₂ desorption, mass transport, and conversion, are detrimentally coupled at the zero-gap MEA interface. Here, we demonstrate that incorporating a dedicated stripping compartment enables the direct supply of CO₂-laden solution to the membrane interface without electrode obstruction, and effectively decouples the mass transport of desorbed CO₂ from its conversion in an interface-modulated three-compartment flow cell (3CFC), by modulating the pressure differential across compartments to drive directed CO₂ transport. The in situ/operando Raman spectroscopy revealed its unique pH-buffering capability near the electrode, contributing to high C₂₊ selectivity and enhanced eRCC performance. This unique platform achieves remarkable stability and selectivity in the direct conversion of bicarbonate across diverse catalysts. At -200 mA/cm², a Cu(OH)₂-derived catalyst achieved an unprecedented C₂₊ selectivity of 52.0%, representing a 17-fold increase from 3.1% in the MEA cell. Moreover, Ag electrodes exhibit long-term stability for more than 155 h at -100 mA/cm² from bicarbonate conversion, in contrast to the rapid increase in H₂ observed in the MEA configuration. The CO selectivity of a Ni single-atom-catalyst from eRCC was dramatically enhanced to 96.7% utilizing 3CFC, compared to 38.0% in the MEA cell. This work presents a new principle for controlling the interfacial chemical environment in complex electrochemical systems.