Effects of Carbon Support Structure and Ionomer Equivalent Weight on Catalyst Ink Rheology and Fuel Cell Performance

ABSTRACT This study investigates how Pt/C catalyst structure, including carbon support porosity and surface properties, and ionomer equivalent weight (EW) affect catalyst ink rheology and coating behavior for polymer electrolyte membrane fuel cells. Four Pt/C catalysts with porous or less porous supports and different surface wettabilities are formulated with short‐side‐chain perfluorosulfonic acid ionomers at three EWs and a fixed ionomer‐to‐carbon ratio. Ink viscosity, viscoelasticity, thixotropic recovery, aggregate size, and slurry resistance are characterized and linked to coating integrity. Pt/C catalysts with porous supports form gel‐like, shear‐thinning catalyst inks with rapid structural recovery, producing relatively uniform catalyst layers, whereas less porous supports yield low‐viscosity catalyst inks prone to cracking. EW effects depend on support properties: Increasing EW raises viscosity for porous hydrophilic catalysts, has little effect on viscosity for porous hydrophobic catalysts, and impairs recovery and coating integrity for less porous‐support catalysts. These results provide practical insight for catalyst ink formulation.