Gas Diffusion Layers for PEM Fuel Cells: Ex and In Situ Characterization

Abstract The gas diffusion layer (GDL), which is basically a carbon-based and wet-proofed porous medium, is a critical component for proton exchange membrane (PEM) fuel cells. This criticality is mainly due to its critical functions, such as governing the transport of both the reactants and by-products, maintaining a delicate balance between the water removal and membrane hydration levels, offering continuous mechanical support to the thin catalyst layer (CL), and providing sufficient pathways for electron transport. Active research has mainly centered on designing the architecture of GDLs; thus, it is essential to shed light on the state-of-the-art architectures of GDLs, the recent advances in the characteristics of GDLs, and ex situ and in situ characterization techniques that have been extensively used. Therefore, this chapter reviews the main characteristics of GDLs (e.g., gas permeability, electrical and thermal conductivity, porosity, and hydrophobicity and hydrophilicity), with a particular focus on commonly used insitu and ex situ characterization techniques and their effects on the performance of PEM fuel cells.