Two-Phase Transport Performance Of Gas Diffusion Layer In Proton Exchange Membrane Fuel Cells:Pore Network Simulation

With the advancement of society and the rapid development of the transportation industry,the shortage of energy and air pollution are becoming more and more serious.It is a hot research topic to seek a new,efficient,clean and reliable green energy source.Proton exchange membrane fuel cells(PEMFCs)can perform chemical reactions directly under high-efficiency catalysts to convert chemical energy directly into electrical energy compared to the intense combustion process of traditional fossil fuels.Because of its high energy conversion efficiency,clean and pollution-free,high reliability and fast start-up,PEMFCs is considered to be a promising new energy source in various areas,including transportation,mobile power,distributed power stations and aerospace.However,the water management problem in the PEMFCs has a critical impact on the performance and life of the fuel cell,and is an important technical challenge for PEMFCs' large-scale commercialization.Gas diffusion layer(GDL)is a key porous component responsible for the reaction gas diffusion and liquid water transfer between catalytic layer and runner in PEMFC.Thus,understanding the influence of pore space structure on two-phase transfer performance in GDL is conducive to optimizing water management and improving battery performance and life.In recent years,the pore network model based on intrusion-percolation algorithm is receiving more and more attention and has been successfully applied to the study of two-phase flow law in porous materials in PEMFCs.In this paper,the effect of the pore structure of gas diffusion backing layer(GDBL)and micro-porous layer(MPL)on its liquid water transfer and reaction gas diffusion is studied from the level of pore scale by pore network model(PNM)model.The main research contents are as follows:1.The stochastically generated numerical models is used to reconstruct the fiber stacking model of GDL with different structures.The two-step search algorithm is used to extract the spatial pore information in the GDL model to construct the TEPN model,and the two-phase flow simulation is based on the model.2.The TEPN model was used to study the effects of fiber radius,fiber density and number of layers on the pore space structure and mass transfer properties of single-layer GDL.In addition,this paper analyzes pore information,fluid transfer chain information and integral of coordination numbers blocked by liquid water in static invasion path of state level in TEPN,and elucidates the underlying interlinks between fiber structure,pore structure and two-phase transport.3.The regular pore network model was used to study the effect of porosity gradient on the two-phase mass transfer performance of bi-layer GDL with MPL.The effects of MPL porosity gradient values(the porosity ratios of the MPL bottom layer and the top layer were 0.38:0.38(no gradient),0.375:0.385,0.37:0.39,0.36:0.4,0.34:0.42,and 0.32:0.4,respectively),porosity gradient thickness of the MPL(30?m,50?m,70?m,and 90 m)and the graded layer MPL neutron number(single,double,three and four)on mass transfer in GDL(MPL + GDBL)are studied separately.Finally,the influence of the porosity gradient in MPL with crack is analyzed.