Molecular Dynamics Study of Ionomer and Water Adsorption at Carbon Support Materials

Molecular dynamics simulations were applied to unravel the microscopic structure of Nafion ionomer and water adsorbed at graphitized carbon sheets. The considered molecular model resembles microscopic interfaces at which current generation proceeds in catalyst layers of polymer electrolyte fuel cells. The analysis of equilibrated interfacial configurations shows that Nafion ionomer forms a thin adhesive film on the graphite sheet. At low water content, water molecules form clusters around sulfonic acid groups. At high water content, a continuous water film wets the ionomer surface. The structural analysis of this model did not provide any evidence for interconnected water clusters existing inside the ionomer film, which implies that hydronium ion transport will occur mainly along hydrated ionomer surfaces.