Membrane-Electrode Assemblies for Electrochemical Reduction of CO2 to Ethylene: Design for Minimal Energy Consumption

Membrane-electrode-assembly (MEA) cells with copper (Cu) cathodes show strong potential for electrochemical CO2 reduction to ethylene (C2H4), but achieving high C2H4 selectivity remains a challenge due to competing hydrogen evolution. This selectivity is highly sensitive to the local microenvironment near the Cu catalyst surface. In this study, a 1-D, multiphysics continuum model is utilized to investigate how MEA cell performance and faradaic efficiency (FE) to C2H4 are affected by both component properties and operating conditions, with particular focus on coupled transport and reaction phenomena. Key parameters include cathode electrochemically active surface area (ECSA) and catalyst layer thickness. Halving catalyst layer thickness increases FE to C2H4 by 2% and lowers the cell voltage by 40 mV. In contrast, a tenfold decrease in ECSA results increases the FE to C2H4 by 7% but leads increase cell voltage at a given current density by 150 mV. This tradeoff occurs because the potential distribution within the cathode catalyst layer is the primary driving force for C2H4 formation. Increased cell voltage also raises the energy cost of C2H4 production. This model framework enables techno-economic assessments and identifies key factors that must be optimized to enable economically viable production of C2H4 via electrochemical reduction of CO2.