Coupling between Adsorption, Structure, and Rheology in Short-Side-Chain PFSA Ionomer/Carbon Black Suspensions in N-Propanol/Water

Abstract The rheological behavior of proton exchange membrane fuel cell catalyst inks arises from the coupled structuring of carbon particles and perfluorosulfonic acid (PFSA) ionomer dispersions, both strongly influenced by solvent composition. Here, the microstructure, ionomer adsorption behavior, and rheology of short-side-chain PFSA ionomer/carbon black suspensions in N-propanol/water mixtures are investigated. Carbon black forms solvent-dependent particle networks that dominate rheology at low ionomer content. Upon ionomer addition, adsorption onto carbon surfaces modifies interparticle interactions and progressively disrupts the network, leading to a continuous transition in flow behavior with increasing ionomer-to-carbon ratio. At high ionomer concentrations, the rheology becomes dominated by a continuous ionomer-rich phase. These results demonstrate that ink rheology is governed by a transition between particle-controlled and ionomer-controlled structuring mechanisms, regulated by adsorption and ionomer organization, with an optimum dispersion regime emerging at intermediate ionomer content.