Preparation Mechanism And Experimental Study Of Cathode Gas Diffusion Layer Of Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cell(PEMFC)has many advantages,including clean and pollution-free,high energy conversion efficiency,suitable operating temperature and high reliability.Therefore,it has been used as an energy conversion device and made rapid development.However,PEMFC is facing many problems at present,especially its technical bottleneck.When the fuel cell works at high current density,the cathode side produces more water,which leads to untimely drainage and easy flooding,so the performance drops rapidly.The microporous layer(MPL)located between the catalyst layer(CL)and the gas diffusion backing layer(GDBL)plays a decisive role in the water management and gas transmission of PEMFC.Therefore,this thesis aims at the technical bottleneck faced by fuel cells.Starting from the material and structure of MPL,the cathode gas diffusion layer(GDL)with excellent performance is prepared to reduce the manufacturing cost of PEMFC and accelerate the commercialization process.The main research contents and results are as follows:(1)In this paper,non-toxic,low-cost anhydrous ethanol is selected as the solvent,the commonly used polytetrafluoroethylene is used as the hydrophobic agent,and the low-cost and easily available acetylene black and Vulcan XC-72 are used as the conductive carbon black to prepare MPL with pore-size gradient GDL.By testing and analysis of physical and electrochemical properties,the difference between graded MPL and commercial MPL,and their respective effects on fuel cell performance and water management are studied.Experimental results show that GDL prepared by spraying not only has good hydrophobicity,but also has lower resistivity.Comparing with commercial GDL,when the humidity is 60%,the maximum power density is increased by 25%,and when the humidity is 100%,it is increased by 12%.(2)The preparation process of graded MPL is studied and optimized.Not all graded MPL can produce positive effects,and the spraying sequence of carbon black slurry seriously restricts the performance by affecting the reasonable pore-size gradient of the graded MPL.By optimizing the preparation process,GDL is sprayed with a layer of acetylene black first,and then a layer of Vulcan XC-72,which has better fuel cell performance at high current density.Comparing with commercial GDL,when the humidity is 60%,the maximum power density is increased by 25%,and when the humidity is 100%,it is increased by 12%.(3)The thickness and hydrophobicity of the GDL with pore-size gradient MPL are studied systematically,and the cell performance is tested under the conditions of 60%humidification and 100% humidification.Experimental results show that the thickness adjustment of MPL increases the number of 0.5-7μm and 20-100μm pores in GDL,which is more conducive to water discharge.Therefore,the thickness adjustment is more favorable to the cell performance under high humidity.While the gradient hydrophobic design makes the MPL of the modified intermediate layer have a certain water-retaining capacity to humidify the reaction gas,which has better effect under low humidity.(4)The pore-size distribution of GDL is optimized by compounding acetylene black and Vulcan XC-72.The experimental results show that the MPL made of composite carbon powder combines the advantages of the two carbon powders and has a more reasonable pore structure.In addition,the pore-size distribution of GDL is further optimized by adjusting the ratio of composite carbon powder.In particular,GDL with 70 wt.% acetylene black and 30 wt.% Vulcan XC-72 showed the best performance.Compared with commercial GDL,the optimization of GDL structure and material composition in this paper has obvious advantages for improving cell performance and improving water management,and provides new ideas and methods for the development of GDL and solving the technical bottleneck of fuel cells.