Characterization of Ionic Conductivity Profiles within Proton Exchange Membrane Fuel Cell Diffusion Electrodes by Impedance Spectroscopy

摘要

Experimental impedance data recorded foroperating cathodes in proton exchange membrane fuel cells havebeen interpreted with the aid of a finite transmission-line modelin which the ionic conductivity of the catalyst layer decreaseswith distance from the membrane. By purging the cathodecompartment of the cell with nitrogen during measurements, theimpedance response becomes dominated by charging of thecatalyst's double layer through the layer's ionic resistance. Fittingof simulated data to the experimental data provides a profile ofthe variation of the catalyst layer's ionic conductivity withdistance from the membrane. The power of this approach isdemonstrated by comparing data for electrodes with the withoutimpregnated ionomer (Nafion). The Nafion-containing electrodeis shown to have a much higher ionic conductivity, and,consequently, has a larger active catalyst area and provides betterfuel cell performance. Furthermore, its ionic conductivitydecreases with distance from the membrane, consistent with thenonuniform Nafion impregnation expected with the immersion method used.