Phase separation modeling of water transport in polymer electrolyte membrane fuel cells using the Multiple-Relaxation-Time lattice Boltzmann method

Abstract

In this study, a reaction-coupled, multiphase, and multicomponent model was developed to simulate the multiphysics transport phenomena in polymer electrolyte membrane fuel cells. The model integrates electrochemical kinetics, hydrodynamics, species transport, and liquid flooding over the entire cell domain, with a specific focus on addressing channel liquid flooding during high-current operations. It also captures the phase transitions of water in fuel cells, that is, evaporation and condensation within the cell components. The multiple-relaxation-time lattice Boltzmann method was used to solve cell-scale reaction-coupled multiphase equations. Moreover, our model could predict a two-phase channel film flow with the formation of a capillary meniscus, which was validated against published experimental polarization curves, a two-phase flow regime, and two-phase pressure drop data. Numerical simulations were conducted under different operating conditions, that is, humidity, temperature, pressure, and stoichiometric flow ratio, to investigate the physicochemical correlations among the local cell performance, liquid distribution, and quantified phase change rates across the computational domain. Furthermore, various in-plane and through-plane absolute permeability combinations were compared to determine the anisotropic liquid transport characteristics in the porous gas diffusion layers. Based on cell performance and channel pressure drop, a figure of merit was established to optimize the fuel-cell operating conditions. This methodology offers an advanced pathway for balancing the dual challenges of water management, thus ensuring the hydration of the ionomeric phase and mitigating the accumulation of excess liquids.