Autothermal Polarization of Membrane Electrode Assemblies – Effect of the Pt Content of the Catalyst and the Thickness of Fuel Cell Catalyst Layer

Laboratory-scale fuel cell testers typically regulate cell temperature via endplate heating cartridges. In practical stack applications, however, temperature control is achieved by cooling systems, making uniform temperature distribution a critical factor in system design and scale-up. To investigate these thermal effects under realistic conditions, autothermal activation and autothermal polarization experiments were conducted. Membrane electrode assemblies (MEAs) were polarized according to the New European Driving Cycle protocol, while galvanostatic electrochemical impedance spectroscopy (GEIS) measurements were performed in parallel to determine R1, R2, and C2 parameters in situ. Three MEA configurations differing catalyst layers were tested: C-60-Pt, C-40-Pt, and C-60-Pt (0.13 mg Pt/cm2), all with symmetrical Pt loadings. A custom-developed spray-gun robot was used for gas diffusion electrode fabrication. Among the samples, the C-40-Pt MEA demonstrated a pronounced break-in effect after 4 h of autothermal activation and achieved the highest current density. While the low-Pt MEA exhibited the lowest performance, it also showed the largest temperature rise during autothermal polarization. Impedance data confirmed that despite similar series resistance, the C-40-Pt MEA had lower internal resistance, while the more porous C-60-Pt showed increased R1. More consistent curve shapes during autothermal conditions compared to fixed-temperature GEIS indicate that temperature adaptability enhances measurement reproducibility.