Abstract
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.
Highlights
JES FOCUS ISSUE ON ADVANCES IN MODERN POLYMER ELECTROLYTE FUEL CELLS IN HONOR OF SHIMSHON GOTTESFELD
In a Proton Exchange Membrane Fuel Cell (PEMFC), inappropriate water management may lead to performance losses[1,2,3] and irreversible electrode degradation.[4,5,6,7,8,9]
Five different samples were prepared by hot-pressing CI films (XC-72, EW 825, ionomer to carbon (I/C) = 0.8) on both sides of an Ethylene Tetrafluoroethylene (ETFE) substrate
Summary
Capillary penetration method for measuring wetting properties of carbon ionomer films for proton exchange membrane fuel cell (PEMFC) applications. Capillary penetration techniques (e.g., Washburn method) have been used to understand the relationship between pore structure, internal wettability and capillarity.[11,12,13,14,15] Percolation tests led to a better understanding of the water transport mechanisms in the GDLs based on the capillary phenomena.[16,17] Based on those experimental investigations, diverse models, including the pore network model developed by Médici and Allen,[18,19,20,21] offered an accurate prediction of liquid water distribution within the GDLs: see literature reviews[22,23] and references therein All these studies have provided useful information to improve water management issues. Li et al.[27] investigated the effects of cathode CL hydrophobicity on the fuel cell performance They demonstrated that the addition of dimethyl silicone oil (DSO) during the ink preparation increased the CL surface contact angle to water as measured using the sessile drop technique. The contact angles were calculated from image analysis using an open access software: Image J
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