Impact of inhomogeneous catalyst layer properties on impedance spectra of polymer electrolyte membrane fuel cells

A physically-based 1D impedance model of the cathode catalyst layer that accounts for inhomogeneous catalyst layer (CL) properties is developed. The impact of locally changing proton conductivity, volumetric double-layer capacity, ORR rate and effective porosity on the characteristics of impedance spectra is analyzed. It was found that a non-constant conductivity and capacity profile within the CL results in a specific fingerprint in the high frequency range of the spectra where at homogeneous conditions a linear 45° branch would be expected. Furthermore, a well pronounced splitting of a high and low frequency loop can be provoked by introducing non-uniformly distributed CL properties. The simulation results show that electrochemical impedance spectroscopy is a valuable tool to investigate the inhomogeneity of the catalyst layer originated by the electrode preparation itself or by degradation processes.