Performance Optimization and Water Management of Polymer Electrolyte Membrane Fuel Cell with Two-Direction Graded Porosity Design of Cathode Gas Diffusion Layer

Abstract

A three-dimensional nonisothermal two-phase flow model is developed to analyze the effects of cathode gas diffusion layer (GDL) porosity variations on the current density distribution and liquid water saturation in a proton exchange membrane fuel cell (PEMFC). Water phase changes among the vapor, liquid, and dissolved phases are considered in porous zones, whereas water transport in the channel is simplified by considering convection only. To investigate the current distribution quantitatively, the standard variance of current density over the cathode catalyst layer (CL) is applied. Aimed at improving the uniformity of current distribution in a cathode CL as well as further decreasing the liquid water in the cathode GDL, the optimization of graded porosity in a cathode GDL is conducted by parametric design in two directions, where one is the flow direction and the other is the thickness direction. Results indicate that compared with uniform porosity and porosity variations along a single direction, optimized porosity variations along two directions could achieve at most 18.3% improvement in current density distribution and a nearly 5% decrease in liquid water saturation in a high-current-density situation (operated at voltage 0.2 V). Thus, by applying porosity variations along two directions, fuel cell performance is improved and cell usable time is extended, which provides guidance for future material design on GDLs.