Transient Techniques for Investigating Mass-Transport Limitations in Gas Diffusion Electrodes

The use of electrochemical impedance spectroscopy and current-interruption techniques with the scope of determining mass-transport limitations in PEFC gas-diffusion electrodes is investigated. The porous electrode is assumed to be composed of spherical agglomerates consisting of a homogeneous mixture of the electrolyte and the electronic phase. The model is applied to the O 2 reduction reaction in the cathode and includes Tafel kinetics for the O 2 reduction, Ohm’s law for proton migration, Fick’s law for O 2 diffusion, and capacitive current due to the contribution of the double layer. A novel impedance is defined, enabling the results to be presented in a simpler manner than with the usual one. It is shown how these transient techniques can be employed to qualitatively separate diffusion from migration effects. The parameter groups that can be quantitatively determined from the processing of experimental data are presented. The effect of O 2 pressure and electrode thickness on the predicted electrode response is also investigated.