THD spectroscopy is an effective method to evaluate non-linearity of the target system that considers the contribution at all higher harmonic frequencies. It can be defined as the ratio of the Euclidean norm of the system response Y of all higher harmonic frequencies to that of the fundamental frequency.
The influence of carbon monoxide poisoning on the platinum anode in a polymer electrolyte fuel cell was investigated using electrochemical impedance spectroscopy (EIS). Therefore, impedance measurements of the cell under constant load were performed at periodic time intervals. Due to the poisoning effect of the carbon monoxide, the system changes its state during the experiment. The reconstruction of quasi causal spectra was made possible using enhanced numerical procedures, especially the time course interpolation and the Z-HIT refinement. The reconstructed impedance spectra show a strong time dependence and exhibit pseudo-inductive contributions at the low frequency part of the spectra which increase during the experiment. The analysis of the spectra suggests that the pseudo-inductive behaviour can be attributed to a surface relaxation process of the anode. Furthermore, the influence of the carbon monoxide on the electrochemical behaviour of the contaminated fuel cell may be interpreted by means of a Faraday impedance in addition with a potential-dependent hindrance of the charge transfer.