Nafion-based membrane electrode assemblies prepared from catalyst inks containing alcohol/water solvent mixtures

• Pt surface area increases with decreasing alcohol content of catalyst solution.
• Pt surface area depends on solubility parameter δ and dielectric constant ε of, catalyst ink solvent.
• Fuel cell performance depends on δ and ε of catalyst ink solvent.

Many researchers have studied the influence on fuel cell (FC) performance of the dielectric constants (ε values) of the dispersion solvents of catalyst ink solutions in the fabrication of Nafion-based gas diffusion electrodes (GDEs). They have reported that Nafion forms colloidal particles in dispersion solvents possessing ε = 3–10, making these solvents suitable for fabricating GDEs with excellent FC performance. In this paper, we study the dependence of both the Nafion ionomer morphology in the catalyst layers and the FC performance of the GDEs on ε and the solubility parameter δ of the alcohol (i.e., methanol and isopropyl alcohol)/water dispersion mixture. The dispersion solvents of the catalyst ink solutions contain 20–100 wt.% alcohol with 23.4 > δ > 11.3 and 78.4 > ε > 19.9. By plotting the FC performance against the ε and δ values of the alcohol/water dispersion solvent mixture, we demonstrate that the FC performance increases with increasing ε and δ values of the catalyst ink dispersion solvents. ε and δ are determined to be better parameters than the compositions of the solvent mixtures for describing GDE performance.

Three-dimensional plots of the maximum power density (PDmax) of the MEAs against the solubility parameter δ and dielectric constant ε values of the alcohol/water solvent mixtures of the Pt–C/Nafion catalyst ink solutions. (▲) Methanol (MeOH)/water solvent mixtures; (△) isopropyl alcohol (IPA)/water solvent mixtures.Figure optionsDownload as PowerPoint slide