Morphology and Transport Characterization of Catalyst Layers for CO 2 Reduction

Abstract

Gas diffusion electrodes (GDEs) help to reduce transport limitations in devices for electrochemical CO 2 reduction. Homogenized modeling of such devices requires input of morphological characteristics and effective transport properties of the porous structure, which can be obtained by pore-scale methods. Due to the small pore sizes and layer thicknesses, such characterization of the catalyst layer (CL) is difficult. In this work, CL structures digitalized by FIB-SEM nano-tomography were analyzed to obtain a set of morphological descriptors and were considered as geometrical domains in direct pore-scale simulations to calculate tensors of effective diffusion coefficient, permeability, tortuosity, and effective ionic and electronic conductivity. The CL properties vary significantly depending on the diffusion and flow direction, and samples of similar composition and synthesis technique exhibit different transport behaviors. The reported results provide a quantitative morphological analysis and a reliable set of effective properties to be used in homogenized device modeling, a net improvement over the most commonly used empirical or analytical formulations. The data set was obtained directly from the pore-scale structure of real CLs and contributes to making device-scale homogenized modeling of GDEs more accurate and reliable.