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

Efficient gas–liquid–solid mass transfer of CO 2 molecules is essential for the performance of the electrocatalytic CO 2 reduction reaction (e-CO 2 RR), yet the unclear dynamic evolution of CO 2 bubbles at the three-phase interface has hindered the understanding of the e-CO 2 RR 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 CO 2 mass transfer with the e-CO 2 RR performance was established, with an average error of 6.14%. Furthermore, the intrinsic coupling relationship among bubble dynamics, interfacial area, mass transfer, and e-CO 2 RR activity is revealed. In this reaction, the mass transfer rate of CO 2 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 CO 2 molecules in e-CO 2 RR and provides a scientific foundation for rational reactor design, process optimization, and scalable electrochemical CO 2 conversion.