Elucidating Bubble-Mediated Mass Transfer in Electrocatalytic CO ₂ Reduction within a Spiral Microchannel Reactor

Efficient gas–liquid–solid mass transfer of CO2 molecules is essential for the performance of the electrocatalytic CO2 reduction reaction (e-CO2RR), yet the unclear dynamic evolution of CO2 bubbles at the three-phase interface has hindered the understanding of the e-CO2RR mechanism. Herein, a new microchannel reactor featuring a spiral channel is developed to control bubble-mediated mass transfer at the three-phase interface. In comparison with conventional serpentine channels, the proposed spiral channel delivers a 34.76% lower pressure drop and a 42.31% higher mass transfer uniformity. A model correlating CO2 mass transfer with the e-CO2RR performance was established, with an average error of 6.14%. Furthermore, the intrinsic coupling relationship among bubble dynamics, interfacial area, mass transfer, and e-CO2RR activity is revealed. In this reaction, the mass transfer rate of CO2 bubbles increases monotonically with the interfacial area, and their total transferred mass exhibits a volcano-type trend with the interfacial area. This work also examines the influence of bubble dynamics on the multiphysics distributions and overpotential evolution. Overall, this work elucidates the mechanistic role of the three-phase interface for CO2 molecules in e-CO2RR and provides a scientific foundation for rational reactor design, process optimization, and scalable electrochemical CO2 conversion.