Modeling Proton Exchange Membrane Fuel Cell Cathode Catalyst Layers with the Lattice-Boltzmann-Method Framework

Abstract

A Lattice-Boltzmann-Method model for a proton exchange membrane fuel cell (PEMFC) electrode has been presented. One of the main challenges in the development of the cathode catalyst layer (CCL) in PEMFCs is the lack of detailed understanding of species transport and how it affects electrochemical performance. Researchers have typically used high level approximations that oversimplify the microstructure of the CCL—these are known as macrohomogenous models. However, as the field has progressed, these idealizations have begun to show their flaws, especially in areas of improving catalytic performance with lower Pt-loadings and non-noble metal catalysts. Previously, the microstructure details needed to build an accurate mesoscale model have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), creating these representations has become possible. Mesoscale modeling in the CCL has been traditionally approached through either the Lattice-Boltzmann-Method (LBM) or electrochemistry coupled Direct-Numerical-Simulation (DNS). These models have been underutilized in the fuel-cell community due to their complexity and resource intensiveness; however, with advances in parallel computing, this has become not only a possibility, but a necessity for modeling phenomena such as low platinum loadings and interfacial effects. The idea behind this model is to study a particular phenomenon – the effect of current density on saturation. While not the focus of this work, LBM can eventually be coupled with DNS in a synergistic modeling approach. This can shed light on the transport and degradation phenomena in PEMFCs, particularly catalyst layer considerations and carbon support corrosion.

Advances in Focused Ion Beam Tomography for Three-Dimensional Characterization in Materials Science

“…The collapse of the porous cathode microstructure was characterized in the work of Star et al [94] by the correlation of electrochemical methods, infrared spectroscopy, and FIB-SEM tomography, showing that the platinum ripening and carbon black corrosion were the main causes of the performance loss. Grunewald and co-authors presented a lattice Boltzmann method model applied to a cathode catalyst layer (CCL), which combines tomography data and mesoscale modeling techniques, to improve the knowledge of the transport mechanisms of the oxygen in the catalyst layer [95]. In an article by Pournemat, a voxel-based Montecarlo model describes the strict relationship between the wettability and pore size distribution on the water distribution within the gas diffusion layer (GDL) and the CCL [96], while Nakajima used FIB-SEM tomography to model the pore network of their hydrophobic microporous layers to evaluate the convective air permeability and oxygen diffusivity [97].…”

“…which combines tomography data and mesoscale modeling techniques, to improve the knowledge of the transport mechanisms of the oxygen in the catalyst layer [95]. In an article by Pournemat, a voxel-based Montecarlo model describes the strict relationship between the wettability and pore size distribution on the water distribution within the gas diffusion layer (GDL) and the CCL [96], while Nakajima used FIB-SEM tomography to model the pore network of their hydrophobic microporous layers to evaluate the convective air permeability and oxygen diffusivity [97].…”