Design Of Distributor And Research On Gas Diffusion Layers In High-Temperature Proton Exchange Membrane Fuel Cells

Fuel cell is a new type of power generation device that directly converts chemical energy from fuel into electrical energy.It is also the fourth mode of power generation after hydropower,thermal power generation and atomic power generation.The power generation principle of fuel cells is that the Gibbs free energy in the chemical energy is converted into electrical energy in an electrochemical way.It is not limited by the "Carnot cycle",and the theoretical working efficiency can reach 85%,which is an efficient way of power generation.Among them,the proton exchange membrane fuel cell(PEMFC)is considered to be one of the most promising technologies of power sources in the 21 st century because of its advantages of high efficiency,low emissions,simple structure and silence.In this work,the main study purpose is the oxygen flow distribution in high-temperature proton exchange membrane fuel cell(HT-PEMFC),and two aspects of the flow field distributor and the gas diffusion layer(GDL)are studied.In the commercial software COMSOL Multiphysics 5.6,a three-dimensional HT-PEMFC model is established for simulation,which is analyzed in the uniformity of oxygen flow,pressure drop distribution,diffusion flux,ohmic resistance and cell performance.The relevant work and conclusions are as follows:Uniformity is one of the essential factors for improving the performance of HTPEMFCs.In the study of distributors,inspired by the human blood circulation system,a new distributor model was established,designed using Murray’s law,and the uniformity evaluated in parallel flow fields.The results indicated that the uniformity of oxygen distribution in the parallel flow field was directly related to the distributor.Traditional distributor will lead to serious heterogeneous oxygen distribution in parallel flow fields and large areas of low oxygen concentration in the catalyst layer(CL).Implementing a new distributor,the power density of the cell was increased by 25.3%,uniformity of oxygen distribution increased by 76.5%,and average pressure drop of the flow field increased by 15.7%.Discussions of theoretical calculations revealed that the average pressure drop was the main factor affecting the uniformity index.Increasing the average pressure drop can improve oxygen consumption and uniformity of oxygen distribution.In addition,this work conducts a comprehensive study on GDL in HT-PEMFCs,homogeneous and heterogeneous porosity models are established,and the effects of GDL thickness and porosity on the electrical conductivity,oxygen distribution,diffusion flux,ohmic resistance,ohmic polarization,and cell performance of HTPEMFCs are discussed respectively.The results indicate that the thickness of GDL will affect the uniformity of oxygen flow and cell performance.Appropriately increasing the thickness of GDL helps to improve the uniformity of oxygen flow in CL.However,when the GDL is too thick,the diffusion flux of oxygen continues to decrease and the ohmic resistance continues to increase,which will lead to a decline in cell performance.Increasing the average degree of porosity can improve the oxygen concentration and the uniformity index of oxygen distribution in the CL.When the average porosity increases from 45% to 65%,the uniformity index increases from 80.2% to 91.9%.Porosity is inversely proportional to electrical conductivity and directly proportional to ohmic resistance.Discussions of the porosity heterogeneity reveal that the average porosity is the main factor affecting the cell performance.The optimal porosity of the GDL falls between 40% and 45%,and the gradient of porosity is small.