Effect of Carbon Corrosion on Wettability of PEM Fuel Cell Electrodes

Large transport resistances at high current densities hinder the proton-exchange-membrane fuel cells from reaching performance-cost-durability targets. Extensive carbon corrosion in the cathode catalyst layers (CCL) has been shown to correlate to pore closures and increase in surface oxides of carbon support, which has been associated with the increase in wettability of CCLs. This study investigated effects of microstructure and surface oxides on the change of wetting properties of CCLs after different accelerated stress tests. The apparent contact angles were measured over a broad range of carbon mass losses at 0.3 mg Pt /cm 2 . The apparent contact angles fell sharply after small extent of carbon loss followed by a plateau, and decreased again after 123 μg/cm 2 (35% carbon support loss). The microstructural changes were characterized by surface roughness (atomic force microscopy) and porosity (focus-ion-beam scanning electron microscopy and thermogravimetric analysis). The surface roughness and porosity were used to parameterize Wenzel's, Cassie-Baxter's, and combined models to elucidate the changes in Young's contact angle. The fittings of the models revealed that the CCLs sustained their wettability after up to 35% of carbon support loss due to the increases in the proportion of hydrophobic fluorocarbon chains on the surface of the CCLs measured from XPS.