Multiphase interfacial transport engineering governs CO₂ availability in liquid-fed bicarbonate electrolysis

Liquid-fed bicarbonate electrolysis offers a promising route for coupling carbon capture with electrochemical CO₂ conversion; however, performance under high-current operation is fundamentally constrained by the availability and transport of in situ–generated CO₂ at the membrane–electrode interface. In these systems, effective reactant delivery is governed by reaction–transport coupling and multiphase flow rather than bulk CO₂ concentration alone. Here, we demonstrate that regulating interfacial morphology and surface functionality enhances local CO₂ retention and phase distribution under convective conditions. Amine-functionalized catalyst layers modify interfacial acid–base conditions and improve CO₂ retention, while microstructured Nafion membranes stabilize localized gas-phase CO₂ holdup zones and mitigate interfacial depletion. Two-phase computational fluid dynamics simulations coupled with electrochemical measurements reveal a direct structure–transport–performance relationship, showing that enhanced superficial CO₂ mass fraction governs sustained activity. The integrated strategy enables selective CO production with Faradaic efficiencies of ~80% at 500 mA cm −2 and stable operation exceeding 160 h. These findings establish multiphase interfacial transport as a critical engineering parameter in bicarbonate electrolysis and provide design guidelines for scalable liquid-fed CO₂ conversion systems. • Multiphase transport limits CO₂ availability in carbonate electrolysis. • Interfacial structuring enhances local gas-phase CO₂ retention. • CFD reveals structure–transport–performance coupling. • Stable CO production at 500 mA cm −2 under liquid-fed conditions.