Colloidal interactions mediated by functional additives play a critical role in the formulation of inks for fuel cells and electrolyzers. In particular, understanding and controlling these interactions is essential for producing uniform, high-quality catalyst layers, which in turn are critical for high power-density performance. This presentation summarizes experiments and supporting theory that explore ionomer-mediated colloidal interactions in model ink systems. Model inks were prepared using polystyrene beads (0.001 wt%) as a model catalyst surface and Nafion ionomers (EW850, EW1000, and EW1100) dispersed in a 1-propanol/water (9:7 w/w) solvent mixture. Five ionomer-to-catalyst (I/C) ratios—1, 5, 10, 100, and 500—were examined to study the concentration-dependent behavior. Total Internal Reflection Microscopy (TIRM) and particle tracking techniques were used to measure the motion of particles both normal and parallel to a nearby boundary. These measurements revealed an attractive depletion force at low I/C ratios, and oscillatory structural forces at higher I/C ratios. An analytical model was developed to describe the observed interactions, with fitted parameters providing insight into the mechanisms by which Nafion mediates colloidal forces. The results show that Nafion induces sensitive, thermally-scaled (~kT) depletion interactions at low concentrations, while structural forces dominate at higher concentrations.
