(129a) Understanding the Performance and Limitations of Membrane-Electrode-Assembly Architectures for the Electrochemical Reduction of CO2

Authors: 
Weng, L. C., Joint Center for Artificial Photosynthesis, LBNL
Bell, A. T., University of California
Weber, A., Lawrence Berkeley National Laboratory
Romiluyi, O., Joint Center for Artificial Photosynthesis, LBNL
The electrochemical reduction of CO2 (CO2R) to value-added products is an attractive technology for tackling the rising atmospheric CO2 levels and storing intermittent renewable energy in chemical bonds. To achieve commercially-relevant CO2R rates (> 100 mA cm-2), gas-diffusion electrodes (GDEs) play an important role as they overcome mass-transport limitations that result from unfavorable CO2/OH- interactions and large diffusion lengths observed in aqueous, planar systems.1 The thin diffusion layer in GDEs, typically in the order of 10 to 100 nm, also allows operation of CO2R in alkaline conditions, which have been shown to suppress the hydrogen evolution side reaction (HER), and reduce the onset potentials of CO2R products such as CO and C2H4.2-5 With the increase in total current density, conventional cell designs for planar electrodes become severely limited by the ohmic drop across the cell, making membrane-electrode assemblies (MEAs) an attractive alternative. MEAs have smaller cell resistances as they do not have aqueous electrolyte compartments and minimal distances between the two electrodes.

In this talk, we present a multiphysics modeling framework for MEA systems performing CO2R. We discuss the performance and limitations of two MEA designs: one with gaseous feeds at both the anode and cathode (full-MEA), the other with an aqueous anode feed (KHCO­3, KOH, water, exchange solution) and a gaseous cathode feed (exchange-MEA). Finally, we draw insights from sensitivity analysis of key parameters such as catalyst-layer loading and porosity, membrane thickness, kinetic rate constants etc. to guide the design of next-generation CO2R devices and elucidate knowledge gaps to inform future research areas.

Acknowledgements
This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. We thank David Larson for providing experimental data for CO2 reduction on membrane-electrode assembly devices.

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