Proton exchange membrane fuel cells (PEMFCs) have garnered considerable attention for transportation applications owing to their high energy efficiency. Understanding their long-term durability is essential because the performance deteriorates over time. The water transport characteristics of the gas diffusion layer (GDL), aged by inserting hydrogen peroxide solutions, are investigated. The dynamics of the water meniscus inside the GDL is visualized via synchrotron phase-contrast radiography, and the temporal variations in the pressure are measured simultaneously. The pressure and time at breakthrough (BT) when the water firstly emerged from GDL were compared. The degraded GDL exhibits a larger BT pressure and requires a longer time to achieve the first water BT than the pristine GDL. Unlike the pristine GDL showing snapoff patterns, water continuously penetrates the degraded GDL representing the piston-like movement, and repetitive increases and decreases in the pressure are not observed. This difference represents the dominant transport mechanisms. GDL degradation induces the loss of polytetrafluoroethylene (PTFE), which is generally used for the effective transport of fuel and water. The PTFE loss reduces the hydrophobicity and pore size, which can increase the actual path length of the water flow. The increase in the BT time and BT pressure, as well as continuous transport, can disrupt fuel supply to chemical reaction sites, thereby deteriorating the PEMFC performance.

Freshwater shortage has been receiving considerable attention, and water harvesting is one of the potential solutions to this water crisis. Several researchers have tried to improve the harvesting capabilities by changing mesh wettability for atmospheric fog harvesting. However, the wettability effect on water harvesting from white plumes has not yet been investigated thoroughly, despite industrial cooling towers being considered as alternative water resources, because of the large amounts of fog plumes generated. In this study, surface wettability was modified with a robust and simple method for practical scaled-up applications, and we explored the influence of mesh wettability on atmospheric and industrial fog harvesting. In atmospheric fog harvesting, both superhydrophilic meshes (SHPMs), and superhydrophobic meshes (SHBMs) were found to improve the harvesting performance, with superhydrophobic treatments providing the best collection efficiency. In contrast, only superhydrophilicity improves the performance in industrial fog harvesting with flat mesh screens. We hypothesize that this research will be useful for mesh design, as it analyzes the influence of mesh wettability on the performance of water collection in both atmospheric and industrial water harvesting.

No abstract

Shortages of freshwater have become increasingly common around the world, and various studies have been conducted to solve this problem by collecting and reusing the water in nature or from factories and power plants that produce large fog plumes. Although the shape of a collection screen is strongly related to its harvesting performance, only flat meshes have been considered in previous studies, and research on the effects of collector structure shapes is severely lacking. In this study, we proposed modified collector structures improving harvesting performances in industrial cooling towers. The screen shape was modified in three steps. First, a concave shape was adopted for the mesh screen to increase the aerodynamic characteristics of the collection structure. Next, a sidewall was installed to collect additional fog from defected flows generated by the concave structure. Finally, to reduce loss during the draining of collected water droplets, the discharge direction of the fog flow was changed to follow the same direction as fog-laden flows in nature. Our results are expected to be useful for collector design in terms of increasing harvesting efficiency in various industrial fields in the future.