Bead Mill for Fuel Cell Catalyst Ink: Why Dispersion Quality Sets the Performance Ceiling. Fuel cell catalyst ink is a dispersion of platinum-on-carbon (Pt/C) catalyst, ionomer, solvent, and water that gets coated onto a membrane to form the electrode layer inside a proton exchange membrane (PEM) fuel cell. Finer, more uniform catalyst particle dispersion generally correlates with higher current density and better fuel cell performance, one study found smaller average part