We report a three‐dimensional (3D), pore‐scale analysis of morphological and transport properties for a polymer electrolyte fuel cell (PEFC) catalyst layer. The 3D structure of the platinum/carbon/Nafion electrode was obtained using nano‐scale resolution X‐ray computed tomography (nano‐CT). The 3D nano‐CT data was analyzed according to several morphological characteristics, with particular focus on various effective pore diameters used in modeling gas diffusion in the Knudsen transition regime, which is prevalent in PEFC catalyst layers. The pore diameter metrics include those based on chord length distributions, inscribed spheres, and surface area. Those pore diameter statistics are evaluated against computational pore‐scale diffusion simulations with local gas diffusion coefficients determined from the local pore size according to the Bosanquet formulation. According to our comparison, simulations that use local pore diameters defined by inscribed spheres provide effective diffusion coefficients that are consistent with chord‐length based estimations for an effective Knudsen length scale. By evaluating transport rates in regions of varying porosity within the nano‐CT data, we identified a Bruggeman correction scaling factor for the effective diffusivity.

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Since the first publications by Hazlett (Transp Porous Med, 20:21-35, 1995) and Hilpert and Miller (Adv Water Res, 24:243-255, 2001), the pore-morphology-based method has been widely applied to determine the capillary pressure-saturation curves of porous media. The main advantage of the method is the simulation of a primary drainage process for large binary images using moderate computational time and memory compared to other two-phase flow simulations. Until now, the pore morphology model was restricted to totally wetting materials or those with a constant contact angle. Here, we introduce a similarly computationally efficient extension of the model that now enables the calculation of capillary pressure-saturation curves for porous media, where the contact angle varies locally within, due to a composite structure.

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The objective of this work is to develop advanced microstructure analysis tools for direct quantification of the key structural properties of complex fuel cell materials. Computationally efficient algorithms have been developed to extract the key structural parameters from measured microstructure datasets of these materials. In addition to determination of the traditional structural measures (e.g., porosity, surface area, phase connectivity), two novel microstructure analysis techniques are introduced for the quantification of pore size and tortuosity distributions. For initial demonstration purposes, the methods developed are applied to a digitally reconstructed sample of the micro-porous layer (MPL) of a polymer electrolyte fuel cell (PEFC). The results produced from these analyses are compared to previously reported experimental and model-derived values where applicable.