PEM Fuel Cell Electrodes Surface Defects Impact on the System Performance

Fuel cell system manufacturing process is not a defect-free process, therefore, the impact o typical defects in the electrodes (i.e. Gas Diffusion Layer (GDL)) surface has to be taken into consideration when the fuel cell system is being designed.

To assess the impact of the defect on the performance, two approaches were taken into consideration. Initially, the fuel cell system was simulated using a unidimensional (1D) dynamic model which took into consideration mass transfer, heat transfer and electrochemical phenomena, and a tridimensional (3D) multiphysics computational fluid dynamics (CFD) model which includes the fluids dynamic in the channels and porous media (electrodes) of the fuel cell system.

The first one was simulated using Matlab® and Simulink to measure possible variations in the system dynamic response, and therefore, its dynamic parameters.  A design of experiment (DOE) approach was proposed to assess the fuel cell physical relevance in the dynamic response model and the results are presented as regressions of the relevant factors.

The second one was used to investigate the impact of the GDL morphology variation in specific locations where its porosity was changed to simulate a blockage or the presence of catalyst uniformities in the catalyst layer (CL) on the internal dynamic variables hard to measure like the current distribution in the Nafion membrane and the pressure in the channels and the electrodes. The second approach was experimental, using a 5 sq.cm PEM fuel cell, the impact of the GDL porosity on the fuel cell system was studied. Also, the system response under different load changes was investigated. After that, experimental results are presented to give a better insight into the phenomena analyzed, mainly on the dynamic system response.

Cracks and catalyst clusters were the main defects analyzed, both of them were observed in new membranes assemblies. To control the defects, new membranes assemblies were tested, and after that, defects were induced using Nafion solution and catalyst powder to emulate the presence of catalyst clusters. For the cracks, some fibers in the GDL cloth were cut to emulate the defect. Membranes now with defects were tested again to compare its performance and detect any performance loss due to the physical changes in the electrodes.

Results indicate a strong correlation between the porosity and the supply air pressure and the system time constants. Also, the impact of the defects was evidenced in the dynamic system response, after step changes in the operating conditions.