Hydrodynamics Determine Tafel Slopes in Electrochemical CO2 Reduction on Copper

The hydrodynamics of electrochemical CO2 reduction (CO2R) systems is an insufficiently investigated area of research that has broad implications on catalyst activity and selectivity. While most previous reports are limited to laminar and CO2-sparged systems, herein we address a wide range of hydrodynamics via electrolyte recirculation systems. We find that increased hydrodynamics at the electrode surface results directly in changes to the ethylene and methane Tafel slopes, demonstrating that mass transport is on equal footing with catalyst active sites in determining reaction mechanisms and the ensuing product distribution. Mass transport is traditionally considered to be in the purview of systems-level engineering, yet the present work shows that CO2R mechanistic work must be considered in the context of the mass transport conditions. We extend our analysis to organic coatings, demonstrating that the films shield the active sites from variability in hydrodynamics and increase the residence time of CO so that it may be further reduced to desirable products.