Electrochemical impedance spectroscopy has become a popular characterisation
method for PEM fuel cells. The method method is used for extracting informa-
tion on the individual losses mechanisms in the fuel cell. There is however still
some disagreement in the scientific community about how the data obtained from
impedance measurements should be interpreted.
The models which are used to reproduce measured impedance spectra and quantify
individual loss components are simple equivalent circuit models which provide no
insight into the actual causes of the recorded impedance spectrum. This report
treats the development of a novel electrochemical impedance model for HTPEM
fuel cells. The model is based on a 2D finite volume approach and incorporates the
effects of cathode mass transport, electrode kinetics and proton conduction.
In order to enable validation of the model a number of polarisation curves and
impedance spectra have been recorded on a BASF Celtec 2100 MEA. The mea-
surements are carried out in the laboratory using a single cell HTPEM test rig. An
attempt has been made to fit the model to the data but no successful fit has been
obtained. Instead the model is validated by comparing the effects of operating
parameter variations on the data and the model results.
In order to improve the understanding of the phenomena which dominate individual
parts of the impedance spectrum a parameter variation study is performed on the
model. The study indicates that some of the interpretations of impedance spectra
presented in the literature are based on incorrect assumptions.
It is concluded that the model developed has potential for becoming a useful tool
in impedance spectroscopy studies providing that sufficient improvements can be
made to enable fitting to experimental data.