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AC impedance modelling study on porous electrodes of proton exchange membrane fuel cells using an agglomerate model

 
: Gerteisen, D.; Hakenjos, A.; Schumacher, J.O.

:

Journal of power sources 173 (2007), No.1, pp.346-356
ISSN: 0378-7753
English
Journal Article
Fraunhofer ISE ()

Abstract
A one-dimensional model of the PEM fuel cell cathode is developed to analyse ac impedance spectra and polarisation curves. The porous gas diffusion electrode is assumed to consist of a network of dispersed catalyst (Pt/C) forming spherically shaped agglomerated zones that are filled with electrolyte. The coupled differential equation system describes: ternary gas diffusion in the backing (O-2, N-2, water vapour), Fickian diffusion and Tafel kinetics for the oxygen reduction reaction (ORR) inside the agglomerates, proton migration with ohmic losses and double-layer charging in the electrode. Measurements are made of a temperature-controlled fuel cell with a geometric area of 1.4 cm x 1.4 cm. Lateral homogeneity is ensured by using a high stoichiometry of lambda(min). The model predicts the behaviour of measured polarisation curves and impedance spectra. It is found that a better humidification of the electrode leads to a higher volumetric double-layer capacity. The catalyst layer resistance shows the same behaviour depending on the humidification as the membrane resistance. Model parameters, e.g. Tafel slope, ionic resistance and agglomerate radius are varied. A sensitivity analysis of the model parameters is conducted.

: http://publica.fraunhofer.de/documents/N-67885.html