| Proton exchange membrane(PEM)fuel cell has many characteristics,such as high efficiency,strong applicability,no pollution et al,and it has been widely used in portable power and electric vehicles,etc.Temperature is an important factor for the performance of PEM fuel cell,and the performance of fuel cell improves with the increasing of temperature.However,due to the special requirements of proton exchange membrane,catalyst and materials,the PEM fuel cell generally works at low temperature environment(below 80℃)at present,there are also some researches for high temperature proton exchange membrane(HT-PEM)fuel cell with the temperature above 100℃.The operating temperature of HT-PEM fuel cell ranges of 120～180℃,and it solves the liquid water management,electrochemical reactivity,CO tolerance and heat utilization problems,but it also puts forward new requirements on the material properties and design of flow fields.In order to understand the work characteristics of HT-PEM fuel cell better,the thesis mainly conducts the following research jobs:Firstly,multi-physics fields directly coupling analysis software was adopted to establish the single cell 3D model of direct way structure of flow field with the condition that working voltage is 0.5 V,permeability of gas diffusion layer were 1.18×1 0-12 m2,1.18×10-11 m2,1.18×10-10 m2 and 1.18×10-9 m2,HT-PEM fuel cells were numerical simulated.The simulation results concluded that the membrane current density,cathode oxygen concentration and the center of cathode flow field pressure changes.Analysis showed that as the permeability increased,it can improve the membrane current density of HT-PEM fuel cells,and the change trend of membrane current density was parabolic;and can effectively reduce the pressure drop of flow field center in cathode,reduce the extra power consumption,improve the gas mass transfer inside the fuel cells,accelerate the electrochemical reaction rate,then improve the output performance of the fuel cells;Secondly,creating two kinds of serpentine flow fields HTPEM fuel cell 3D steady state model with different flow structures,analyzing the influence of flow pattern of serpentine flow field and electrical conductivity of proton exchange membrane on the output performance of fuel cells.The simulation results concluded that the output performance of HT-PEM fuel cell with three serpentine flow field was better than that of single serpentine flow field,by increasing the number of serpentine field parallel port bend to reduce the gas flow number,it can not only control the import and export pressure drop in a reasonable scope,but also can make the distribution uniformity of reaction gas in flow field better;the increase of electrical conductivity can enhance the conductivity of proton exchange membrane,reduce the loss of resistance in process of mass transfer,improve the output performance of fuel cells;Thirdly,in the same operating conditions,HT-PEM fuel cells with different combination of flow fields(two kinds of single flow fields and two kinds of mixed flow fields)were simulated,it was concluded that both the oxygen concentration and pressure of the flow field center in cathode reduced gradually along the direction of gas flow,and the change mainly occured at the corner and the gradient of the flow fields;performance of fuel cells was mainly affected by the shape of flow field in cathode,and the performance of serpentine flow field gradient was superior to the ordinary serpentine flow field;considering the output current density,distribution uniformity of gas and extra power consumption,the output of serpentine flow field gradient compared with the best performance,secondly,the mixed flow field which was combined by ordinary serpentine flow field in anode and serpentine flow field gradient in cathode,thirdly,the ordinary serpentine flow field and the mixed flow field which was combined by serpentine flow field gradient in anode and ordinary serpentine flow field in cathode was the worst. |
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