Quantifying Heterogeneities at the Mesoscale via Tomography-Based Pore-Scale CO2 Electroreduction Modeling

Electrochemical CO 2 reduction (eCO2R) in gas diffusion electrodes (GDEs) is strongly governed by the complex interplay between catalyst-layer (CL) mesostructure, devicelevel wetting conditions, and local electrochemical environments. Here, a tomographybased multiphysics modeling framework is developed for a Ag CL in a GDE. The threedimensional CL morphology is reconstructed, while two cross-sectional images (>10 µm wide and 4 µm thick) enable simultaneous segmentation of the CL and microporous layer (MPL). Morphology and transport properties are extracted. Subsequently, the crosssections are considered as as pore-scale domains in a modified Poisson-Nernst-Planck model, coupled with homogenized descriptions of the unresolved section of the MPL and the carbon fiber layer support. We show that device flooding affects GDE performances nonlinearly, and CO 2 solubility at the gas-liquid interface is affected due to variations in ionic strength at the interface. Direct comparison between the two cross-sections reveals differences in CO current density arising directly from local morphological differences. The pore-resolved simulations show spatial variations in CO 2 availability, pH, and local current densities that are not captured by conventional volume-averaged descriptions. Finally, we quantify the effect of including different permittivity formulations on local and device-level conditions. Results highlight the importance of understanding the variability of pore-scale conditions to understand and optimize performances of devices for eCO2R.