Novel Gas Diffusion Layers with Patterned Wettability

Inside a polymer electrolyte fuel cell (PEFC), the water management is rather complex: on one hand, the membrane needs a certain hydration state in order to ensure a sufficient proton conductivity; on the other hand, excessive water leads to blocked gas pathways with increased mass transport losses. Liquid product water is transported by capillary forces [1] from the catalyst layer throughout the gas diffusion layer (GDL) towards the gas flow channels, in opposite direction of oxygen diffusion.

Under high current densities, the water production rate becomes high and the volume occupied by water can dramatically decrease the accessibility of oxygen resulting in mass transport limitations (so-called flooding). To address this issue, we are developing new GDLs with patterned wettability [2]. The idea is to define engineered hydrophilic pathways to force the transport of liquid water through them and vacate the rest of the volume for the transport of gases, decreasing the tortuosity.

The proposed synthetic method bears significant advantages compared to other reported approaches such us laser perforation [3] or local application of hydrophobic coating [4]: full flexibility in the pattern design without compromising the mechanical integrity, smaller hydrophilic regions can be defined (100 µm achieved) and the ratio between hydrophilicity and hydrophobicity can be tuned. Figure 1 shows the water preferentially accumulating in the hydrophilic regions.

In this talk, we will present details about the synthetic method together with ex-situ characterization results: chemical information based on energy dispersive x-ray (EDX) spectroscopy mapping (Figure 2) and water distribution with neutron radiography. Additionally, first operando results using the multicell setup [5] with pulsed gases analysis (PGA) will also be presented.

[1] U. Pasaogullari, et al., Int. J.Electrochem. Soc., 151 (2004), pp 399-406.

[2] P. Boillat, et al., European Patent Application EP15165515.6, (2015).

[3] D. Gerteisen, et al., J. Power Sources, 177 (2008), pp 348-354.

[4] R. Koresawa, et al., J. Power Sources,271 (2014), pp 16-24.

[5] P. Oberholzer et al., Electrochem. Commun., 20 (2012), pp. 67-70.