In this work, capillary rise experiments were performed to assess the wetting properties of carbon-ionomer (CI) films. The samples were attached to a micro-balance and then immersed into liquid water to (i) measure the mass gain from the liquid uptake and (ii) estimate the (external) contact angle to water (typical value around 140°). The results showed that drying the CI films under low vacuum significantly impacted the CI film wettability. The influence of the ionomer content on the CI films' wettability was investigated with various ionomer to carbon (I/C) ratios: 0.8, 1.0, 1.2 and 1.4. No significant variation of the contact angle to water extracted from the capillary rise experiment was measured. However, water uptake increased with the I/C ratio suggesting a more hydrophilic behavior. This observation was in good agreement with the measurement from the sessile drop method showing a slight decrease of the contact angle to water: from 155°for an I/C of 0.8 to 135°for I/C = 1.4.

Proper water management in Polymer Exchange Membrane (PEM) fuel cell is important to achieve high performance. Understanding the percolation of the produced water at the cathode catalyst layer (CL), is critical for any robust water management technique. The CL consists of a complex structure to allow reactants to pass through and reach the reaction catalyst site. The complex structure is made by a support structure (mostly carbon) that allows the transport of electrons, an ionomer that conducts protons, and voids that have the double role of oxygen breathing and exit paths for the generated water. In this work, a pseudo-Hele–Shaw experimental setup is used to investigate immiscible fluid displacement inside the CL under controlled conditions. Since water can be retained by ionomer, making it swell and caused a shift in the pore size distribution, fluor-inert is used as a working fluid. The evolution of percolation pressure and the projected area of the injected fluid are recorded simultaneously.

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Understanding and modeling of mass transport limitations in the catalyst layers in PEM fuel cells remain a challenge despite decades of commercial development. That challenge has led to the development of a novel ex-situ test to characterize mass transport resistances in these extremely thin porous layers. This test characterizes radial percolation of gas and liquid at varying fluid injection rates and relative humidities.Liquid percolation exhibits a dominant capillarity influence at low injection rates with lower final wetted areas and saturation as compared to high injection rates. Changes in relative humidity have a significant effect on percolation behavior for both gas and liquid. There is a significant jump in resistance when the relative humidity exceeds 65%.

Percolation testing and contact angle measurements have been used to investigate the role of relative humidity on structure, mass transport, and wettability of a PEM fuel cell catalyst layer and membrane. Four samples were tested, two catalyst layers and two membranes. Structure and mass transport changes in the catalyst layers resulting from RH changes were studied in terms of percolation pressure. A clear change in the structure between low and high RH conditioning was observed. Relative humidity (RH) cycling also impacted percolation pressures with an indication of catalyst layer cracking. In addition, RH effect on wettability of both catalyst layers and membranes was studied by measuring contact angles of sessile drops.