Molecular Dynamics Study of Ionomer Adsorption at a Carbon Surface in Catalyst Ink

Ionomer adsorption at the surface of a graphite sheet in a solvent-saturated environment was examined using molecular dynamics simulations. The amount of ionomer adsorbed on the graphite surface greatly depended on the equivalent weight (EW) of the ionomer and the alcohol content in the solvent. The maximum ionomer coverage was obtained in water-rich solvent for low EW ionomer, while the addition of alcohol to the solvent was necessary to enhance adsorption of high EW ionomer. The ionomer coverage at the surface with ionized functional groups was lower than that of the bare graphite surface, which indicated a significant effect of the electrostatic repulsive interaction between negatively charged functional groups and sulfonic acid groups on the ionomer adsorption. The effect of the alcohol content and EW of the ionomer on ionomer coverage still remained even in the presence of strong electrostatic interactions between sulfonic acid groups and the functionalized carbon surface.