Modelling analysis of heterogeneity of ageing in high temperature polymer electrolyte fuel cells: insight into the evolution of electrochemical impedance spectra

- Aged EIS show an enlargement of cathode charge transfer and mass transport features.
- Uniform ageing of cathode ECSA does not affect impedance spectra.
- Heterogeneity of ageing increases charge transfer and mass transport resistances.
- Heterogeneity of ageing at channel and CL scales can reproduce aged EIS

Degradation of catalyst electrochemical active surface is a major issue that hinders polymer electrolyte fuel cells commercialization. Several degradation mechanisms that have been reported in the literature are known to result in heterogeneity of ageing, whose effects on performance loss have not been previously investigated. In this work experimental and theoretical methodologies are combined to provide an insight between the effects of heterogeneity of ageing and the evolution of electrochemical impedance spectra. Experimental results collected during a 6000 hours degradation test indicate an increase of cathode charge transfer and mass transport resistances, consistently with cyclic voltammetry that reveals about 60% loss of cathode catalyst active surface. A physical based model is developed and validated to demonstrate that uniform cathode ageing does not to affect the evolution of impedance spectra. On the other side, it is shown that non-uniform ageing of cathode active area improves the agreement with experimental data. The evolution of the polarization curves and impedance spectra recorded during 6000 hours degradation test is critically discussed by including heterogeneity of ageing.