Gas Diffusion Layer Deformation And Its Effect On The Transport Characteristics And Performance Of Proton Exchange Membrane Fuel Cell

Polymer electrolyte membrane fuel cell (PEMFC), which converts the chemicalenergy of fuels into electrical energy directly through electrochemical reactions, iswidely considered as one of the most promising clean energy power sources becauseof its high energy efficiency, low operating temperature, high power density,capability of quick start-up, and clean and quiet operating characteristics. However,when all of the components of a PEMFC are assembled together, the gas diffusionlayer (GDL) porous structure may be destroyed, which strongly affect the watertransport characteristics and performance of PEMFC. In this study, numericalsimulation and experimental methods are used to investigate the GDL deformationand its effect on the transport characteristics and performance caused by the assemblyforce. The work can be summarized as follows:(1) The stress-strain relation for GDLs under different assembly forces ismeasured experimentally. It shows that the Young’s Modulus is5.53MPa for GDL.And the GDL porosity decreased from0.78to0.2under the600N assembly force.The permeability is changed as much as an order of magnitude.(2) A mechanical deformation model is developed and solved numerically withthe finite element method. The different GDL deformation profiles under variousassembly forces are obtained, and the porosity, permeability and other transportparameters are predicted, so as to provide accurate physical parameters for thethree-dimensional multi-phase transport model for PEMFCs. The results indicate thatthe GDL under the land changes significantly while the central region under the flowchannel almost has no deformation.(3) The performance of the inhouse-assembled PEMFCs under various operatingconditions is investigated in order to find the optimal operating conditions. It is seenthat the PEMFC performance is better when the inlet pressure is0.2MPa, the inlettemperature is70℃, and the inlet relative humidity is100%. The results show that theperformance of the PEMFC is not fitted with the rise of assembly force, especially forthe high current density, the performance was even decreased.(4) The spatial distribution of GDL porosity, permeability and other transportparameters obtained from the mechanical deformation model are implemented in athree-dimensional multi-phase PEMFC model. The basic conservation equations, the heat and mass transport equations for gas and liquid, electrochemical reaction and thewater phase change are included in this model to analyze the cell performance and thewater distribution caused by the assembly forces. The results indicate that thickerGDLs result into lower water content in the GDL structure, and can sustain a largerassembly force without the risk of “electrode flooding”; but obtain a poorer cellperformance. Although thicker membranes lead to lower cell performance, itbrings/causes the increasing water content of anode CL. The anisotropy of GDLtransport parameters are further considered in the three-dimensional multi-phase flowPEMFC model. This effect is largely ignored in previous modeling studies. And inthis study, it is shown that the anisotropic electricity conductivity has the greatesteffect on the performance of PEMFC, the anisotropic permeability strongly affects thewater transport, and the anisotropic thermal conductivity makes the temperaturedistribution more uniform.