Insights into Oxygen Transport Properties of Partially Saturated Gas Diffusion Layers for Polymer Electrolyte Fuel Cells

Abstract

A multimodal approach was used to investigate the oxygen transport resistance of gas diffusion layers (GDLs) for polymer electrolyte fuel cells (PEFCs) under different temperature and humidity conditions. This study aimed to gain further insights into the oxygen transport properties of partially saturated GDLs by relating the GDL structure to water generation and transport. Morphological characterization of GDLs was performed by synchrotron X-ray computed tomography and mercury intrusion porosimetry. The oxygen transport resistance of dry and wet GDLs was measured directly using the Wicke-Kallenbach type diffusion cell. The observed transport properties of dry GDLs were correlated with the pore morphologies. Moreover, it was found that the direct measurement approach characterized the oxygen transport resistance of wet GDLs, eliminating the contribution of the catalyst-coated membrane, and captured the impact of water saturation level in GDLs on the oxygen transport properties. An electrochemical approach using limiting currents was used to study the effect of water generation on oxygen transport resistances. The oxygen transport resistance of wet GDLs at the PEFC cathode was evaluated by varying gas pressures and GDL thicknesses. Results show that the oxygen transport resistance of wet GDL depends on the local water saturation created by liquid water. Our comprehensive studies provide insights to derive the optimal evaluation method for a given purpose, leading to a rational and sustainable material design for GDLs of PEFCs.