Structure Optimization Of PEMFC Gas Diffusion Layer And Flow Field Based On Multi-physical Field Coupling

Proton exchange membrane fuel cell(PEMFC)is a complex dynamic system with multiple physical fields,phases and scales.During the operation of the fuel cell,the reaction gas from the outside to the reaction area underwent multi-scale transport processes,such as flow field-diffusion layer and catalytic layer.There are many factors affecting material transport and fuel cell performance,among which the porosity and flow field structure of diffusion layer are also the key factors,and have become the focus of researchers today.Reasonable porosity structure of diffusion layer or flow field structure can improve the problems of low reaction gas transmission efficiency,large internal pressure loss in the flow passage,water flooding of the fuel cell,and improve the overall performance of PEMFC.In order to improve the above problems,based on the coupling analysis software of multiple physical fields,the porosity and flow field structure of the diffusion layer are optimized.The specific research contents are as follows:(1)Influence of porosity of diffusion layer on material transport and overall performance of fuel cell.The distribution of oxygen concentration,liquid water concentration and current density in the three directions of the composite porous diffusion layer with porosity varying along the thickness,width and length of the dc channel PEMFC was studied.The results show that compared with the diffusion layer with uniform porosity distribution(=0.5),the porous diffusion layer with varying porosity along the thickness,width and length of the diffusion layer can improve the material transport capacity and drainage capacity of the diffusion layer and obtain better fuel cell performance.(2)The influence of new flow field structure on the performance of fuel cell.The influence of the flow field of rectangular groove with different number(N=0、1、3、5、7)uniformly distributed on the axis of the flow channel and the flow field of different types(rectangle、triangle、wave)on the performance of PEMFC was studied.Under the operating temperature of 70℃ and operating pressure of 1 atm,the velocity vector of the new flow field,the pressure distribution in the flow passage,the distribution of oxygen content in the cathode and the electrical properties were analyzed.The results show that in the case of reasonable pressure drop in the channel,the number of rectangular grooves N=5 is the most suitable new flow field structure.The addition of different types of grooves improved the fuel cell performance,among which the wavy groove had the best effect,followed by the rectangular groove and the triangular groove had the least effect on the battery performance.(3)The influence of flow field size and structure on fuel cell performance.The parallel flow field of fuel cell is simulated with different channel widths,different rid widths,number of different serpentine channel and different corner structure types in the serpentine channel.The results show that: in the parallel flow field,the ratio of the width of the fuel cell to the width of the rid is 1:1,which is the ideal size ratio.The increase of the width of the parallel flow field has less effect on the performance of the fuel cell than the increase of the width of the rid.Compared with the single,double and triple serpentine channel,the pressure loss of the three serpentine channel is relatively small.When the serpentine channel fuel cell corner is designed with rounded corners,the overall flow rate of the fuel cell can be improved and the fuel cell performance can be improved.