Two-Phase Dynamics and Hysteresis in the PEM Fuel Cell Catalyst Layer with the Lattice-Boltzmann Method

Abstract

In this work, a Lattice-Boltzmann-Method (LBM) model for simulating hysteresis in a proton exchange membrane fuel cell (PEMFC) electrode is presented. One of the main challenges hindering study of the cathode catalyst layer (CCL) in PEMFCs is the lack of understanding of two-phase transport and how it affects electrochemical performance. Previously, the microstructure details needed to build an accurate mesoscale model to examine such phenomena have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), reconstruction of the complex porous media has become possible. Using LBM with these representations, the difficult problem of catalyst layer capillary hysteresis can be examined. In two-phase capillary hysteresis, both the equilibrium saturation position as well as its absolute value depends on the wetting history. Based on the models, it is ascertained that at lower capillary numbers, the liquid begins to undergo capillary fingering—only above a capillary pressure of 5 MPa, a regime change into stable displacement is observed. As capillary fingering does not lead to uniform removal of liquid, the prediction is that because high capillary pressures are needed to change to the regime of stable displacement, wicking is not as effective as the primary means of water removal.

The Effect of Pore-Scale Two-Phase Flow on Mineral Reaction Rates

“…For instance, in geometry b, a few simulations at the high and low flow velocities especially with large v w /v nw showed coalescence of the gas bubbles, which resulted in significantly lower saturation in the reactive zone. Bubble coalescence and breakup are widely observed phenomena that are dependent on fluid properties, velocities, and geometries (Jo and Revankar, 2009;Paulsen et al, 2014;Chen et al, 2017;Mahabadi et al, 2018;Ren et al, 2020;Grunewald et al, 2021). These processes are accompanied by the re-organization of the fluid-fluid interface and can introduce perturbations in the velocity field.…”

“…From a macroscopic perspective, as capillary number (Ca) increases, interface migration transitions from the capillary fingering regime with more random local movement to the viscous fingering with more stable displacement (Toussaint et al, 2012;Li et al, 2019;Grunewald et al, 2021). However, Ca alone does not provide a good description of the fluid-fluid interface dynamics (Armstrong et al, 2015), which is more sensitive to pore-scale roughness/morphology at low capillary numbers (Toussaint et al, 2012).…”

“…This results in a Reynolds number (Re) of 1-10 and a capillary number (Ca) of ∼10 −4 -10 −3 . The Ca-values are within the range that is relevant for typical reservoirs (Satter and Iqbal, 2016) and battery systems (Grunewald et al, 2021). At the outlet, the zero gradient boundary condition is applied for both flow and transport (Table 3).…”

“…As a result, LNAPL is spread vertically following local drainage-imbibition cycles, which in turn affects the degradation and thus the fate of the contaminants (Ngien et al, 2012;Pan et al, 2016;Govindarajan et al, 2018). The interactions between two-phase flow and electrochemical reactions have also been identified as a research priority for the design of effective fuel cells, as gas bubbles (of e.g., H 2 and O 2 ) can be generated by side reactions during charging and affect power generation (Chen et al, 2017;Grunewald et al, 2021).…”

Understanding Electrolyte Filling of Lithium-Ion Battery Electrodes on the Pore Scale Using the Lattice Boltzmann Method

“…Similar to molecular dynamics simulations, where molecular interactions are modeled to study, e.g., wetting phenomena [22][23][24] or transport processes [25,26], it uses fluid-fluid and solid-fluid interaction forces to model interfacial tension and adhesion forces, respectively [20]. So far, LBM has been successfully applied to investigate water transport and hysteresis effects in catalyst or gas diffusion layers of polymer electrolyte membrane fuel cells [27][28][29][30][31][32][33].…”