Water management of proton exchange membrane fuel cells : two-phase flow simulation in gas diffusion layers and channels

Abstract

Proton exchange membrane fuel cells are a promising green energy conversion technology for clean and sustainable power generation. However, effective water management remains a critical challenge. Water produced by electrochemical reactions can accumulate within porous electrodes and flow channels, leading to flooding that impedes the reverse transport of reactant gases to the reaction zone, thereby reducing fuel cell efficiency. A comprehensive understanding of two-phase flow behavior within gas diffusion layers and channels is essential for optimizing water removal strategies and enhancing overall performance. Despite extensive experimental and numerical investigations, the detailed dynamics of liquid–gas transport and interfacial interactions in these components remain inadequately characterized.
This thesis presents a series of high-fidelity numerical investigations of two-phase flow evolution in gas channels and gas diffusion layers, conducted using the volume of fluid method within the OpenFOAM v7 framework. The research investigates the water-gas interactions with a focus on (i) effects of bipolar plate surface wettability and water inlet configuration on channel water transport and pressure drop; (ii) the influence of fiber shape and additive content on microstructure topology and transport properties; and the role of liquid inlet configurations and gas outlet boundary conditions of gas diffusion layers on water transport. To facilitate these analyses, a stochastic reconstruction algorithm was developed to generate detailed fibrous representations of the gas diffusion layer, enabling a systematic study of fiber diameter, curvature, and additive structure content on capillary pressure and water saturation.
Experimental characterization of proton exchange membrane fuel cells reveals performance degradation concomitant with a transition of bipolar plate surface wettability from hydrophobic to hydrophilic following extended operation. This degradation process accelerates under continuous use of hydrophilic plates and correlates with increased transport resistance, suggesting an elevated flooding probability. To verify this hypothesis, two-phase flow simulations conducted in a straight gas channel demonstrate that hydrophobic channel surfaces promote more rapid water evacuation, minimize water accumulation, and stabilize pressure-drop fluctuations more effectively than hydrophilic surfaces.
In addition, two-phase flow simulations of gas diffusion layer and channel assemblies reveal that fiber diameter and curvature exert a pronounced influence on liquid transport. At constant porosity, increasing the fiber diameter enlarges pore spaces, precipitating earlier liquid breakthrough and increasing water retention within the gas diffusion layer, while reducing saturation levels in the adjoining hydrophilic flow channels. Conversely, increasing fiber curvature introduces a greater proportion of smaller pores, increasing capillary pressure and promoting liquid spreading, which in turn enhances overall water saturation. Multi-sample analyses, employing consistent stochastic reconstructions, indicate that variability in liquid transport arises principally from the random stacking of fibers. Nevertheless, this variability may be mitigated by increasing fiber curvature. In addition, the introduction of the additive predominantly decreases the fraction of smaller pores. As a result, at relatively low additive loadings, the additive exerts minimal influence on water saturation under highly hydrophobic conditions. However, once the additive concentration exceeds a certain threshold, its effect on water removal cannot be neglected, yielding a notable reduction in water retention. Comparative evaluation of distinct inlet configurations further demonstrates that the spatial distribution and size of liquid entry profoundly alter two-phase transport. A full-area inlet yields broad wetting coverage, whereas localized inlets generate discrete flow pathways. Under a localized inlet scheme, permitting reverse gas outflow at the diffusion layer lower corners alters liquid propagation patterns, underscoring the necessity of accounting for counter-flow effects in two-phase flow studies.
This work is expected to enhance the understanding of two-phase interaction within gas diffusion layers and gas channels. The findings emphasize the pivotal roles of fiber geometry, additive content, channel surface wettability, and liquid inlet arrangement in governing transport efficiency. However, to offer practical guidance for manufacturing and application, the present findings should be integrated with complementary studies on gas diffusion layer functionality, including gas transport, electrical conductivity, and thermal conductivity, as well as the compatibility between different components.

• author: Yang, Danan
• supervisor: Martin Andersson; Himani Garg
• organization: Heat Transfer; LTH Profile Area: The Energy Transition
• publishing date: 2025-06-02
• type: Thesis
• publication status: published
• subject: Energy Engineering
• ISBN: 978-91-8104-577-2
• ISBN: 978-91-8104-578-9
• language: English
• LU publication?: yes
• additional info: DDefence details Date: 2025-08-29 Time: 10:15 Place: Lecture Hall M:B, building M, Ole Römers väg 1F, Faculty of Engineering LTH, Lund University, Lund. External reviewer(s) Name: Stroh, Alexander Title: Dr. Affiliation: Karlsruhe Institute of Technology, Germany.
• id: 1a970fda-249e-4a28-8df8-9a550c6ed371
• date added to LUP: 2025-06-02 20:46:57
• date last changed: 2025-06-16 13:22:13