Dual-Beam FIB/SEM Characterization, Statistical Reconstruction, and Pore Scale Modeling of a PEMFC Catalyst Layer

Abstract

The three-dimensional structure of a PEMFC catalyst layer (CL) was obtained using a dual beam Focused Ion Beam/Scanning Electron Microscope (FIB/SEM). Lower order statistical functions such as porosity and two point correlation functions calculated from the FIB/SEM data were used in the numerical reconstruction of a multi-phase CL domain. A 'carbon-sphere-based' initial seed structure, when optimized by simulated annealing, produced a structure for which the two point correlation function matched with the FIB/SEM data with very high fidelity. The reconstructed CL domain with its phase-resolved nano-structure was used to perform numerical simulation and predict effective transport properties. The coupled partial differential equations governing the reactive transport of charged and neutral species in the CL were discretized based on the finite volume method and solved implicitly using parallel computing. The simulated values of the effective oxygen and water vapor diffusivity, proton and electron conductivity, and thermal conductivity were in reasonable agreement with measured data reported in the literature. A parametric study was performed to investigate the impact of inaccessible pores-a feature that is not resolved experimentally. The simulations indicate that the properties most sensitive to the presence of inaccessible pores are the effective O 2 and H 2 O diffusivities and the effective proton conductivity.

Microstructure Reconstruction and Characterization of the Porous GDLs for PEMFC Based on Fibers Orientation Distribution

“…Reconstruction of a heterogeneous material to obtain the microstructure can be performed using different experimental methods. Recently, X‐ray nano/micro‐computed tomography (CT) and focused ion beam/scanning electron microscopy (FIB/SEM) have been widely used to reconstruct the porous medium 3D microstructures. Ostadi et al created GDL‐microporous layer (MPL) assembly through X‐ray nano tomography and FIB/SEM, respectively.…”

Quantification of artifacts in scanning electron microscopy tomography: Improving the reliability of calculated transport parameters in energy applications such as fuel cell and battery electrodes

“…However, rather than to solve physically correct models (for instance MaxwelleStephan two phase flow instead of Fick's law in a PEMFC catalyst layer [7] or the questionable application of Ohm's law at the nanometer scale), this study intends to sensitize the reader to carefully question the reliability of FIB-SEMt based parameter calculations.…”

Method to improve catalyst layer model for modelling proton exchange membrane fuel cell

“…With a few exceptions [13][14][15], the most common method used in the literature to describe these resistances is the spherical agglomerate model by idealising the CL as a packing of isolated spheres [16,17]. This idealisation not only oversimplifies the CL structure [4,[18][19][20][21], but is also self-defeating. For example, its assumption of isolated and non-touched spheres physically makes the CL insulate to electrons as electrons can only transport through the carbon grains.…”