Numerical Study Of Structure Deformation And Performance Of PEMFC In Humidity Environment

Proton Exchange Membrane Fuel Cell(PEMFC)is considered as one of the most promising power devices,but its durability,cost and performance have yet to be resolved.Temperature and humidity affect catalyst activity,membrane mechanical mass transport and performance of fuel cells.Cracks,even delamination will be produced in the catalyst layer/membrane interface under temperature and humidity cycling during repeated startup and stopdown of fuel cell,which will reduce the performance of fuel cell.Based on the Finite Element Method(FEM),the structural deformation of fuel cells in different relative humidity and water content is studied in this paper.The water absorption behavior of the proton exchange membrane is studied experimentally,and the expansion coefficient is brought into the whole cell model of PEMFC.The influence of structure deformation on the transport characteristics of membrane electrode assembly and performance of the fuel cell in different relative humidity and water content is studied.The software COMSOL is used to calculate the influence of different crack lengths and crack locations on the mass transport and performance of the fuel cell.In addition,the stress-strain curves of Catalyst Coated Membranes(CCM)are tested,and Young’s modulus of the catalyst layer is obtained.The simulation results show that the relative humidity affects the mechanical properties of the membrane,resulting in the change of membrane structure and uneven distribution of membrane stress,and the larger the relative humidity is,the larger the deformation of the membrane is.The fuel cell performs best when the relative humidity is 70% in the range of 30% to 90%.Considering the influence of water content λ,the deformation of the membrane increases with the increase of λ.In the low current density region,the structure change caused by λ has little effect on the performance of fuel cells.In the region of high current density,the performance of fuel cell is best when λ is 12,and worst when λ is 15.The existence of cracks of the catalyst layer/membrane interface leads to uneven distribution of current density.The larger the current density is,the more obvious inhibition of cracks on electrochemical reaction is.The performance of the fuel cell decreases with the increase of crack length.When the crack is at the outlet,it has the greatest influence on the performance of the fuel cell and the worst performance.Compared with the fuel cell without cracks,the current density decreases by 15.52%.The experimental results show that the linear strain of the membrane increases with the extension of immersion time in liquid water,but when immersion time reaches a certain extent,the strain of the membrane will reach a relatively stable state.Tensile experiments show that Young’s modulus of CCM increases with the increase of strain rates.At a low strain rate,the morphology of the CCM catalyst does not change significantly.At a higher tensile rate,the surface morphology of CCM changes,and its surface is interlaced.Young’s modulus of the catalyst layer is lower than that of the membrane.