Ionomer Dispersions: Solvent Addition Sequence Matters

In this work we show that, when creating ionomer dispersions, in addition to the solvent composition, it is critically important to also consider the ionomer’s solvent exposure history as this has an impact on its final dispersion state. By variation of the solvent addition sequence to the ionomer, the retainment of properties gained from previous solvent exposure states is illustrated. The order of solvent addition to the ionomer has a direct impact on the dispersions’ final properties, such as the aggregate size and viscosity. Variations in dispersion properties subsequently affect catalyst inks, which in turn can lead to different coating qualities and distinct electrochemical behaviors. Notably, in fuel cell experiments, differences in the mass transport properties are observed, especially among electrodes with higher ionomer content, either due to different Knudsen diffusion processes in the catalyst layer or local O2 diffusion through the ionomer films.