Preparation And Experimental Study Of A New Gas Diffusion Layer For Proton Exchange Membrane Fuel Cells

The complexity of proton exchange membrane fuel cell(PEMFC)is that its working process involves many physical chemical process and multifunctional components.Among various components,the gas diffusion layer(GDL)is an indispensable component.When air is used as an oxidant,it plays an important role in determining performance,durability,and dynamic characteristics.The GDL is an integral component,typically located outside the catalyst layer.In addition to providing mechanical integrity for membrane electrodes(MEA),GDL also performs many key tasks in the operation of PEM fuel cells,such as gas distribution,water transportation,heat conduction,and electrical conductivity.At present,there is still a problem with PEMFC that as the electrochemical reaction proceeds,liquid water is continuously generated on the catalyst layer(CL)side of the cathode.If it cannot be removed in time,it will hinder the transmission of the reaction gas,leading to the inability of the electrochemical reaction to proceed normally,resulting in a significant decrease in battery performance.Research has shown that adding a layer of Microporous layer(MPL)structure to GDL can effectively improve water flooding conditions,so MPL with good performance is of great significance for improving the performance of PEMFC.This article does not rely on carbon paper,but uses electrospinning to prepare an independent microporous fiber membrane as MPL,and studies its structure.The GDL composed of microporous fiber membrane and carbon paper is placed on the cathode side with high performance requirements for electrochemical testing,analyzing the improvement effect of electrospinning MPL on the performance of fuel cells.The effect of electrospinning MPL on improving the performance of fuel cells is analyzed.By improving the structure of anode GDL,the impact of its gradient hydrophobic structure on the performance of fuel cells was analyzed,while reducing manufacturing costs and preparation requirements to meet the requirements of commercial production as soon as possible.The main research contents and results are as follows:(1)To explore the optimal solution concentration of electrospun polyacrylonitrile(PAN)precursor,spinning process control parameters,and heat treatment temperature and time,use electrospinning technology to prepare microporous fiber membranes,analyze the impact of different heat treatment temperatures on fiber morphology,and analyze the pore structure of microporous fiber membranes.Test it as a cathode GDL composed of MPL and commercial carbon paper in a fuel cell.Based on the electrochemical performance under40% and 60% humidity conditions,obtain the basic thickness for the subsequent optimization study of the nanofiber film,and compare its performance with commercial GDL to determine the practicality and subsequent optimization perspective of the nanofiber film as MPL.The receiving distance between the injection pump and the drum is 20 cm,and the drum speed is 300 r/min.The microporous fiber membrane prepared in the laboratory has a good pore structure,and the microporous fiber membrane with a thickness of 50 μm as MPL has good performance at low and medium humidity,which is similar to the performance of commercial GDL and has good practicability.(2)Based on the optimized electrospinning parameters for preparing PAN,the preparation process was improved to further treat the microporous fiber membrane with a basic thickness to prepare a microporous composite membrane.The microporous composite membrane was evaluated through tests such as resistivity,water contact angle,and pore size distribution to determine that its conductivity and hydrophobicity were improved without affecting its pore structure.The optimal content of PTFE to improve the hydrophobicity of microporous composite membranes was determined through electrochemical performance testing and analysis under low,medium,and high humidity conditions.The performance of electrospinning MPL was compared with commercial GDL in low,medium,and high humidity,and the role of electrospinning MPL in improving the performance of PEMFC was analyzed.The experimental results show that the conductivity and hydrophobicity of the microporous composite membrane are significantly improved after high-temperature carbonization and hydrophobic treatment.The performance of the GDL15 sample with a PTFE content of 15% is better than that of commercial GDL at low,medium,and high humidity,especially when operating under high current density conditions,the difference is most significant.(3)Using a spray coating process to improve the structure of the anode GDL,a twolayer MPL with gradient hydrophobic ability was prepared using conductive carbon black,PTFE,and PVP.During the experiment,electrochemical tests were conducted on the anode GDL samples prepared in the laboratory,and compared with commercial 29 BC to analyze the impact of the new MPL on battery performance.The hydrophobic ability of the twolayer MPL structure was analyzed through physical properties such as water contact angle,and the self humidifying effect of the gradient hydrophobic structure was analyzed.The test results show that there are significant differences in the hydrophobicity of the bilayer MPL structures prepared in the laboratory,and they have a certain self humidifying effect.They can store a portion of water to humidify the reaction gas,which is more conducive to improving the efficiency of proton transport and allowing the battery to display better performance.Therefore,the optimization of the preparation process and structure of GDL in this article has more significant advantages than commercial GDL in improving the performance of fuel cells.Moreover,the independent analysis of the structure of MPL has provided a new idea for GDL in improving the development direction of water and gas management of PEMFC.