Preparation And Performance Study Of Gas Diffusion Layer For Pemfc

The water transport and gas diffusion in the proton exchange membrane fuel cell(PEMFC)are important factors that affect the PEMFC performance,and the corresponding component is gas diffusion layer(GDL).The traditional GDL is mainly composed of microporous layer and carbon paper.Microporous layer has mostly small pores and carbon paper has single large pores.The process of combining the carbon paper and the microporous layer will produce sudden changes pore size at the contact.And it will affect the water transmission efficiency.In order to solve this problem,a new gas diffusion layer(GDL)was prepared by spraying method and Squeeging method.Compared with the commercial GDL29BC by Japan Toray Company,the influence of the preparation process on the GDL structure and PEMFC performance was studied.The main work is as follows:1.This article first prepared a double microporous layer GDL with a graded pore size structure.The microporous layer near the carbon paper side uses calcium carbonate(CaCO3)as a pore former,and then it is soaked in dilute hydrochloric acid to remove CaCO3.In this way,pores will be left in the original position of CaCO3,and a microporous layer with controllable pore size can be prepared by changing the content of CaCO3 and the ultrasonic time of the mixed solution.The microporous layer on the side of catalyst layer is prepared by traditional mixing method of carbon black and polytetrafluoroethylene,and finally GDL with gradient pore size double microporous layer structure is obtained.The preparation of graded pore size GDL can improve the pore size distribution of GDL,and can optimize the best pore size interval under the premise of controllable pore size,which is not only conducive to water transmission but also conducive to gas diffusion.2.The preparation process was further optimized by adjusting the thickness of gradient pore size GDL and carrying out hydrophilic and hydrophobic modification by rolling.It is found that GDL with thickness of 240 ?m has the best water vapor management ability.When the humidity is 60%,the limiting current density of GDL under the hydrogen and oxygen environment test condition is 6.127 A/cm2,which is 22.6%higher than that of GDL29BC;When it is 100%,the limiting current density is 6.844 A/cm2,which is 30%higher than that of GDL29BC.When the anode GDL with double microporous layer structure is subjected to gradient hydrophilic and hydrophobic treatment,reasonable ratio of carbon black and PTFE can be selected to obtain the best PEMFC performance.When the PTFE:carbon black=3:7 in MPL near the carbon paper side and PTFE:carbon black=1:9 in the MPL near the catalyst layer(CL)side,the self-humidifying GDL under the condition of 40%humidity,power density is 0.23 W/cm2 higher than GDL29BC.The cathode gradient pore size GDL and anode self-humidifying GDL can obtain good PEMFC performance in both hydrogen oxygen environment and hydrogen air environment.3.Using trimethylethoxysilane as the precursor of hydrophobic material and graphene as the conductive material,a continuous electrospinning method for preparing conductive-hydrophobic composite fiber membranes has been developed.The composite fiber membranes can be independently used as MPL in PEMFC.Solve the problem that the MPL in traditional GDL must be covered on the carbon paper support layer.4.A comparative study found that the GDL prepared by the spray coating method has better PEMFC stability and greater limiting current density than the squeegeing method.The former is easier to ensure the uniform mixing of the spray solution and reduce the surface roughness;but the oxidation resistance of the GDL needs to be improved to ensure the durability about PEMFC.5.It is proposed that the capillary pressure difference in GDL determines its internal liquid water transmission efficiency,and it is used to analyze the influence of GDL preparation process,pore size distribution,thickness and its hydrophilicity and hydrophobicity on PEMFC performance.