A review of gas diffusion layers for proton exchange membrane fuel cells-With a focus on characteristics, characterization techniques, materials and designs

Proton exchange membrane (PEM) fuel cells are at the dawn of commercialization. Their operation and design characteristics, hence their performance, are closely linked to the multiphase transport of mass, heat, and electricity in the cell constituents, a critical of which is the gas diffusion layer (GDL). The GDL's transport capability is represented by its effective transport properties: an effective diffusion coefficient for the diffusional transport of mass, absolute and relative permeabilities for the convective transport of mass, effective thermal conductivity for the heat transport, and effective electron conductivity for the electricity transport; in addition, surface wettability impacts the transport of liquid water. These transport properties depend on the GDL's mechanical, morphological, microstructural, and physical characteristics, which are in turn controlled by its materials and design parameters. This review article therefore focuses on the insights and comprehensive understanding of three critical issues of the GDLs: (i) their morphological, microstructural, and physical characteristics, (ii) ex- and in-situ characterization techniques for the determination of their effective transport and mechanical properties, and (iii) frequently used materials and design strategies and their relevant influences on the effective transport properties in order to achieve reliable and durable performance of PEM fuel cells with high power densities. (C) 2019 Elsevier Ltd. All rights reserved.