Many researchers have studied the influence on fuel cell (FC) performance of the dielectric constants (epsilon 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 epsilon = 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 epsilon and the solubility parameter delta 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 > delta > 11.3 and 78.4 > epsilon > 19.9. By plotting the FC performance against the epsilon and delta values of the alcohol/water dispersion solvent mixture, we demonstrate that the FC performance increases with increasing epsilon and delta values of the catalyst ink dispersion solvents. epsilon and delta are determined to be better parameters than the compositions of the solvent mixtures for describing GDE performance. (C) 2013 Elsevier B.V. All rights reserved.