Impact of GDL structure and wettability on water management in polymer electrolyte fuel cells

A key performance limitation in polymer electrolyte fuel cells (PEFC), called the mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. The cathode gas diffusion layer (GDL) is a primary contributor to mass transport loss owing to the blockage of available pore space by liquid water thereby rendering hindered oxygen transport to the active reaction sites in the electrode. The GDL, typically a fibrous non-woven carbon paper or a woven carbon cloth, thus plays an important role in the water management of a PEFC. This Feature Article provides a systematic description of the development of pore-scale models coupled with realistic microstructural delineation as well as micron-resolution imaging techniques to study the profound influence of the underlying structure and surface wettability on liquid water transport and interfacial dynamics in the fuel cell GDL. A pore-network model and a two-phase lattice Boltzmann model coupled with stochastic generation of GDL microstructures are elaborated. Concurrently, optical diagnostics of water dynamics at GDL interfaces and X-ray micro-tomographic imaging of liquid water distribution inside the GDL of an operating fuel cell are discussed.