Active water management for proton exchange membrane fuel cells using integrated wicks and electroosmotic pumps

Fuel cell vehicles offer the potential for increased energy security and significant reductions in oil consumption and greenhouse gas emissions. However, realizing economically feasible and reliable fuel cells remains a significant technical challenge. One important technological barrier is effective water management for proton exchange membrane (PEM) fuel cells. Proper water management ensures necessary membrane hydration while preventing flooding. Common water management strategies include using flow channels with a high pressure gradient and operation with high air stoichiometric ratios. Unfortunately, high flow rates and pressures create a large air delivery parasitic load, complicates the balance of plant (i.e. supporting systems), and reduce system efficiency.;We have developed an active water management system that decouples water removal from oxidant delivery to enable the use of low air flow rates and parallel channels with low hydraulic resistance. The system uses a porous carbon flow field as an integrated wick which passively redistributes water within the fuel cell. We hydraulically couple the wick to a small, external electroosmotic (EO) pump which actively removes excess water from the channels and gas diffusion layer (GDL). EO pumps are well suited for fuel cells because they are compact, have no moving parts, and their flow rate scales with area.;We investigate the unique characteristics of an EO pump coupled with an unsaturated wick using a multiphase, capillary flow model. The results of the model demonstrate the capacity of the wick to prevent flooding by redistributing water. Moreover, the model reveals the significant influence of the wick's capillary pressure on EO pump flow rate. We also present an engineering model that characterizes the scaling of EO pumps and wicks with PEM fuel cells. This model depicts the favorable scaling of EO pumps with fuel cells and suggests that this system can be scaled to fuel cells of all sizes while maintaining parastic loads below 1%.;Our experimental studies investigate water management with both simple, always on and active EO pump control strategies. We resolve the relationship between the water removal rate and the prevention of flooding, as well as the timescale for recovery from flooding. As part of this work, we identify two significant passive water management mechanisms introduced by the wick. First, with adequately high pressure gradients in the air channels, the wick supports sufficient water flow to prevent flooding. Second, the wick can be used to passively humidify dry gases. However, we demonstrate that the EO pump is necessary to enable the robust operation of parallel channel cathode architectures under all operating conditions. The EO pump can properly manage water while consuming less than 0.5% of the fuel cell power. At an efficient, low air stoichiometric ratio of 1.3, the EO pump increases the maximum power density of the fuel cell by 50% over a conventional graphite fuel cell plate.