Influence of FEP nanoparticles in catalyst layer on water management and performance of PEM fuel cell with high Pt loading

In this study, fluorinated ethylene propylene (FEP) nanoparticles were added to catalyst layer (CL) to facilitate excess water removal from the triple phase boundary in high Pt loading (1.2 mg/cm2) proton exchange membrane fuel cell (PEMFC) electrodes. The loading of FEP in the catalyst ink was varied from zero to 30 weight percentage. High-performance electrodes for anode and cathode were prepared by ultrasonic spray coating technique with a commercial catalyst containing 70 wt. % Pt on carbon. Different membrane electrode assemblies (MEAs) were prepared in order to differentiate the influence of hydrophobic nanoparticles on water transport and cell performance. In the first configuration (MEA1), FEP nanoparticles were added to both anode and cathode catalyst layers (cCLs). In the second configuration (MEA2), FEP nanoparticles were added only to cCL. PEM fuel cell tests were carried out at both H2/O2 and H2/Air gas-feeding modes. Impedance spectroscopy results have revealed the influence of FEP nanoparticles on reaction kinetics and mass transport limitations. The addition of FEP nanoparticles decreased Pt utilization due to the isolation of Pt particles, therefore, cell performance decreased. Electrochemical impedance spectroscopy results have shown increasing back diffusion rate of water, and diminishing flooding at cathode GDL at high airflow rate. FEP nanoparticles in the cCLs of 10FEP_C, 5FEP_C at H2/O2 feeding mode and in the CLs of 5FEP_AC, 5FEP_C at H2/Air feeding mode provide meso-macro hydrophobic channeling, which mitigates flooding compared to conventional catalyst layers. For anode and cathode catalyst layer including 30 wt. % FEP nanoparticles (30FEP_AC), capillary pressure increased due to high hydrophobicity, accordingly, liquid water concentration at anode catalyst layer/membrane interface decreased and this caused membrane dehydration.