Study On Mass Transfer And Electrochemical Characteristics In Cathode Of PEM Fuel Cell

Proton exchange membrane fuel cell(PEM Fuel Cell)has attracted the attention of scholars due to its high energy efficiency and pollution-free advantages.PEM fuel cell becomes the new energy power generation device with good application prospects because of its advantages of small size,high power density,low noise,fast start-up speed,green and high efficiency.At present,few researches on PEM fuel cells combine the effects of preload and water management on internal mass transfer.The research on PEM fuel cell water management,especially the research on the detailed characteristics of liquid water distribution in the porous area of the cathode,pays less attention.Therefore,this article focuses on analyzing the effects of preload,cathode humidity and flow field structure on the performance of PEM fuel cells.In this paper,a three-dimensional,steady-state,two-phase,constant temperature PEM fuel cell model is established based on the theory of mass transfer,charge transfer and solid mechanics.The model was meshed,coupled with three physical fields of porous media reaction flow,secondary current distribution and solid mechanics using the method of finite element analysis.This paper analyzed the performance changes of PEM fuel cell under different operating conditions and structures after verifying the validity of the model in order to provide a theoretical basis for improving the performance of PEM fuel cell.Firstly,the solid mechanics model was combined with mass transfer and electrochemical model to simulate the effects of different preload forces on the stress,displacement and effective porosity distribution of gas diffusion layer(GDL)in PEM fuel cell,and the effects of preload forces on the mass transfer and charge transfer of GDL were obtained.The results showed that the GDL region under the ridge was subjected to the action of preload force leading to the deformation occur and the porosity decreased.With the increase of preload force,the oxygen diffusion was affected,and the generated water was difficult to be discharged,resulting in excessive liquid water.The current density was higher in the GDL region below the ridge,and the current density concentration existed at the junction of the channel and the ridge.When the preload force was 2.0MPa,the PEM fuel cell had the best performance.On this basis,the influence of cathode gas humidity on PEM fuel cell performance was analyzed.The results showed that under the same preload force,with the increase of cathode gas humidity degree,oxygen reacted continuously to generate water,and the water content increased gradually.When the humidity reaches 80%,liquid water was produced.When the liquid water saturation was high,the current density also increased,and the battery performance reached the best under the condition of 100% humidity.However,when the preload force was 3.0MPa,the battery gradually produced enough liquid water,and the excess liquid water actually slowed the upward trend of current density.The battery flow field structure had a great influence on the flow of reactants and products,the transfer of water,and the stability of battery performance.The stress distribution of the serpentine flow field was more uneven.As the flow channel went up and down,the mass transfer distribution in the GDL region presented a hump-like fluctuation.When the gas turned into the second flow channel,most areas showed a state of low oxygen and high water concentration.At the same time,the results showed that the limiting current density in the serpentine flow field model had not been greatly improved,and there was also a phenomenon of current concentration.As the voltage decreases to 0.4-0.2V,the current density of the serpentine flow channel change greatly locally.The serpentine structure improved the air intake resistance in the flow channel,reduced the uneven distribution of water,and made the current density distribution more uniform,thereby improving the battery performance.