A series of parameters affecting the catalytic layer microstructure in polymer exchange fuel cell electrodes have been evaluated. The deposition of the catalytic layer in the gas diffusion support is shown to depend not only on the ink deposition method but also on the characteristics of the solvent used to disperse both the catalyst and the Nafion ionomer. The solvent viscosity and its dielectric constant are two important factors to control for the catalytic ink preparation. In particular, the solvent dielectric constant is shown to be directly related to the electrode performance in single cell tests. (c) 2005 Elsevier B.V. All rights reserved.