Nafion Distribution in Gas Diffusion Electrodes for Solid‐Polymer‐Electrolyte‐Fuel‐Cell Applications

The location of Nafion R in solid‐polymer‐electrolyte‐fuel‐cell electrodes was investigated by porosimetry and scanning microprobe analysis. At low Nafion loadings, the polymeric electrolyte uniformly fills the micro‐ and macropores of the electrode structure and increases its ionic conductivity. The pores are completely filled in the range from 0.8 to 1.0 mg of Nafion/cm 2 of electrode, and further addition of polymer results in the formation of a film on the external surface of the electrode. This film causes an additional resistance in series with the ionic resistance in the active layer. Impedance spectroscopic measurements of electrodes with different Nafion loadings provided evidence for a variation of ionic resistance with the amount of polymer. The comparison of impedance data with polarization tests indicates that, at least for our formulations, the ionic resistance is the main factor which controls the electrochemical performance.