Effect of the pore size variation in the substrate of the gas diffusion layer on water management and fuel cell performance

Abstract

The gas diffusion layer (GDL) is a key component of a proton exchange membrane (PEM) fuel cell due to its role as a pathway for fuel, air, and water. GDL determines the mass balance and water management in the PEM fuel cell. Thus, an investigation of the optimal structural characteristics of the GDL with improved water management is important to ensure high performance of the PEM fuel cell. In this study, a PEM fuel cell model that considers the structural characteristics of GDL is developed, and the various the GDL structural characteristics are analyzed and validated. Specifically, the effects of pore size variation in the substrate of the GDL on water management and cell performance are investigated. Two GDL samples with different pore sizes are evaluated according to the porosity, pore size, thickness, and internal contact angle to understand the basic structural characteristics of the GDL. The GDL structural parameters with the basic characteristics are incorporated into the developed model. The cell performance is predicted to be relative to the two-phase mass transport inside the GDL. The characteristics of the micro-porous layer (MPL) and MPL penetration part are found to be affected by the variation in the macro-pore size of the substrate. The water management capability of the GDL varies with these differences with respect to water retention and removal characteristics. Under the condition of relative humidity (RH) 100%, the averaged saturation value of the MPL and MPL penetration part of the GDL with small macro-pore in the substrate is 18.8% higher than that of the GDL with large macro-pore in the substrate. The cell performance is also affected by the operating conditions of relative humidity and current load. The voltage of the GDL with small macro-pore in the substrate at the current density of 1.6A/cm2 is 10.3% lower than that of the GDL with large macro-pore in the substrate under RH 100%.