Modeling Chemical Microenvironments in Porous Copper Electrodes for CO₂ Reduction at Elevated Current Densities

Electrochemical CO 2 reduction (CO 2 R) presents a promising pathway toward the reuse of CO 2 emitted during the production of industrial commodities ( e.g., cement, steel, and plastics) to form value-added commodities and fuels at ambient temperatures and pressures with renewably generated electrons. Copper (Cu) catalysts demonstrate the ability to convert CO 2 to multicarbon (C 2+ ) products. Additionally, 3-D structured porous Cu electrodes can facilitate the operation of CO 2 R to C 2+ at significantly elevated current densities by enhancing the delivery of CO 2 to catalytic active sites on Cu, offering the potential to translate lab-scale understanding to industrial operation. Nonetheless, there still exist selectivity limitations in porous electrode systems due to poor control of the chemical microenvironment, ( i.e., the local pH, CO 2 activity, and CO intermediate management), in these complex electrodes. Therefore, resolving microenvironment in porous Cu electrodes will be critical to advancing these systems towards industrialization. In this talk, we explore the use of continuum modeling to resolve and understand the effects of mass transfer and chemical environment in electrochemical CO 2 reduction in porous Cu electrodes. We explore two scenarios of porous Cu electrodes performing electrochemical CO 2 reduction. The first is the operation of a device employing a bipolar membrane (BPM) in reverse bias, wherein modeling reveals that the proton flux generated by the BPM substantially lowers the pH of the porous electrode and promotes selective CH 4 and HCOOH generation. The second is the use of a micro-structured porous electrode that employs an anion-exchange membrane and more selectively generates C 2+ products. 2-D modeling reveals heterogeneities in the porous electrode enable hotspots of increased pH that locally enhance C 2+ selectivity. Ultimately, this talk underscores the powerful ability of continuum modeling to resolve microenvironments at spatial resolutions beyond what is achievable experimentally, as well as to link changes in microenvironment to changes in local selectivity. These simulations will rationalize and guide the engineering of microenvironment in next-generation porous electrodes for CO 2 reduction to C 2+ products at industrial scales.