Numerical Study Of The Effect Of Proton Exchange Membrane Fuel Cell Structure And Parameters On Its Performance

As the energy and environmental crises become increasingly severe,mankind has been exploring new energy sources and technologies to accommodate green and sustainable development.Proton Exchange Membrane Fuel Cells(PEMFC)are considered to be the most promising power generation system in the future with the advantages of high energy efficiency,no pollution,no noise,and fast start-up.However,as of now,PEMFC still has many shortcomings,which makes its commercial application challenging.In this paper,a single cell model is used to study the polarization performance curve,mass and heat transfer,and current density distribution of the cell using the multi-physics field simulation software COMSOL Multiphysics5.6for both the flow channel shape and the structural parameters.The main studies are as follows:(1)Analyze the effect of cell substance distribution and activation polarization distribution on the overall and local performance of the cell.The results indicate that,overall,the increase in electrode activation polarization has a greater effect on the catalytic performance of the cell.Locally,the current density distributions under the runner and under the rib are strongly influenced by the activation polarization and oxygen distribution,respectively.The distribution of current density mainly shows a gradual decrease along the gas direction,and the current density under the rib is significantly higher than that under the flow channel.For the flow mode of the cell,two flow states,co-flow and counter-flow,are mainly analyzed in this paper.From the V-I polarization curve and P-I curve of the cell,the current density at 0.4 V is increased by 10.8%under counter-flow relative to co-flow,and the peak power density phase is increased by 11.9%.The average current density is 1140 A/m~2 higher than that of the co-flow state due to the better fuel utilization in the counter-flow state.And the counter-current flow helps the convective heat exchange of the battery,which greatly reduces the battery temperature.(2)In order to improve the effect of concentration polarization on the cell performance,different runner shapes(rectangular,elliptical,trapezoidal,dovetail)are designed to reduce the concentration polarization loss of the cell.Among them,the polarization performance curve of the dovetail runner is optimal,and its ultimate current density is improved by 12.5%.The dovetail flow path also has the most uniform oxygen distribution.For the current density distribution,the average current density(A/m~2)at the CL-PEM interface for the four models at an operating voltage of 0.4 V is11750,11648,11506,and 11893,respectively.The average current density of the dovetail model is 387 A/m~2higher than that of the trapezoid,and the current density uniformity of the dovetail model is higher.At the same time,the convection effect of the dovetail flow channel facilitates the discharge of generated water.(3)To study the effects of GDL thickness and porosity on PEMFC,GDL thickness was selected from 0.1 mm to 0.6 mm,GDL porosity from 0.3 to 0.8,and a gradient porosity model with linear increasing(0.3→0.8)along the gas flow direction was designed.The results show that the effects of both the thickness and porosity of GDL on the cell performance curve are significant with increasing current density.The smaller the thickness of the GDL,the more favorable the mass transfer of the cell.However,the smaller the thickness of the GDL,the more uneven the oxygen distribution.The ohmic polarization loss tends to increase linearly with increasing GDL thickness.The current density tends to increase and then decrease with the increase of GDL thickness,in which the current density is the largest at the GDL thickness of 0.2mm,and the current density on the anode/cathode film surface increases by 14.1%and12.7%,respectively.For GDL porosity,as the GDL porosity increases(where gradient porosity is calculated as the average value of 0.55),the molar fraction of oxygen at the GDL-CL interface becomes higher,and the gradient porosity model has the most uniform oxygen distribution.The current density increases with increasing porosity,where the gradient porosity model has the most uniform current density distribution.