Hydrophilic microporous layer coatings for polymer electrolyte membrane fuel cells

Abstract

Polymer electrolyte membrane (PEM) fuel cells are energy conversion devices that are promising components of a sustainable energy system. However, conventional fuel cells suffer from performance degradation at low humidification. To address poor performance under low humidity conditions, we investigate the effect of custom hydrophilic microporous layer (MPL) coatings on liquid water distributions in gas diffusion layers (GDLs), observed in operando using X-ray synchrotron radiography. The visualization was performed during low humidity operating conditions at 60°C, with inlet gas relative humidity (RH) of 50%. Hydrophilic MPLs were coated onto commercial hydrophobic GDLs, and electrical output and simultaneous liquid water measurements were measured, using a fuel cell test station and X-ray synchrotron radiography respectively. The hydrophilic materials showed lower values of membrane resistance (quantified by high frequency resistance) compared to the benchmark hydrophobic GDL. The relatively lower membrane resistance was attributed to improved membrane hydration under low humidity conditions. Correspondingly, the catalyst layer (CL)-MPL interface contained larger quantities of liquid water with the addition of the hydrophilic coating. However, excess liquid water at the cathode side of the GDL led to high oxygen mass transport losses at high current densities. Understanding gained from this study can be used to optimize wettability of the MPL to operate the fuel cell at low or no external humidification.