A microfluidic approach for measuring capillary pressure in PEMFC gas diffusion layers

A dearth of experimental capillary pressure data limits our understanding and optimization of liquid water transport in PEMFC gas diffusion layers (GDLs). A microfluidic device and method is described for measuring the capillary pressure as a function of liquid water saturation for these thin porous materials with complex, heterogeneous wetting properties. A sample sandwich (hydrophilic membrane–GDL–hydrophobic membrane) is key for probing the entire hydrophilic and hydrophobic pore volume of the GDL during sequential liquid intrusion and gas intrusion experiments. The capillary pressure curves for an as-purchased Toray 090 and two differentially-processed Avcarb P75T GDLs were evaluated; each material displayed highly repeatable, but quantitatively different, room temperature capillary pressure curves that matched qualitative differences in their macroscopic wettability. The measurements show that hysteresis between the liquid intrusion and gas intrusion curves is significant. For example, both the Toray and fully wet-proofed Avcarb GDLs appear hydrophobic during most of the liquid intrusion curve and hydrophilic during most of the gas intrusion curve. The implications of this work for water management, and future device designs and experiments are described.