Gas Diffusion Layers for PEM Fuel Cells

QC 2026-10-22

Abstract

Proton exchange membrane fuel cells (PEMFCs) are electrochemical energy conversion systems that convert the chemical energy of hydrogen directly into electrical energy. Gas diffusion layers (GDLs) facilitate reactant transport, water management, and electrical and thermal conduction. Their effective properties depend on material architecture and compression, while their influence on cell performance depends on flow-field geometry and operating conditions. This thesis investigates these relationships through experimental characterization, X-ray computed tomography, continuum modelling, and surrogate-assisted multi-objective optimization.

The thesis provides new insights into how substrate architecture, mechanical properties, and water invasion influence GDL function. The native fiber-binder architecture affected the distribution of subsequently applied polytetrafluoroethylene (PTFE), demonstrating that nominal loading alone is insufficient to describe its distribution within the material. GDL material recovered after approximately 20,000 h of stack operation exhibited differences in pore structure, external wettability, and capillary water invasion relative to the pristine material. Water saturation was higher in the aged material at low capillary pressures, whereas the opposite occurred at higher pressures. Nevertheless, the relative diffusivity–saturation relationships remained broadly similar. These findings distinguish differences in water uptake at a given capillary pressure from differences in the fractional reduction in gas diffusivity at a given saturation.

Material characterization revealed a strong dependence on compression. The measurements informed constitutive relations used in a physics-based continuum model to describe local compression-dependent properties. Through-plane elastic stiffness had the largest mechanical influence on predicted performance within the investigated parameter range, while shear stiffness became more influential with increasing channel width. The effect of stiffness on current uniformity depended on flow-field geometry, supporting the selection of mechanical properties according to rib–channel dimensions. Mean current density was primarily associated with through-plane oxygen transport, whereas current non-uniformity was more strongly associated with lateral transport beneath the ribs.

Joint optimization of GDL properties and flow-field geometry quantified the trade-offs between mean current density, current uniformity, and electrical contact resistance. The analysis showed how under-rib oxygen transport and electrical contact resistance jointly influence the current distribution and constrain design selection. Across changes in operating conditions, design rankings remained comparatively stable despite reduced accuracy in absolute performance predictions. For most investigated conditions, limited additional simulations supported continued use of previously identified designs, reducing the need to repeat the complete optimization.

Together, these findings provide a physical basis for screening candidate GDLs and prioritizing material properties according to assembly compression, flow-field geometry, and performance requirements within the investigated conditions

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