| As a gas diffusion layer(GDL)substrate material,carbon paper is one of the important components of proton exchange membrane fuel cells(PEMFC),which plays an important role in collecting fluid and supporting catalysts,and its performance will directly affect the electrochemical performance of fuel cells.In this paper,three kinds of carbon paper produced by Freudenberg from Germany,JNTG from Korea and Toray from Japan were tested and analyzed were tested and analyzed to preliminarily understand the differences in electrical conductivity,air permeability,and crystal structure;then,the raw materials from polyacrylonitrile(PAN)based carbon fiber nonwoven fabric and pitch based carbon fiber(MPCF)made in the laboratory were used to investigate the effects of the amount of carbon fiber,the concentration of impregnating agent phenolic resin,and graphitization temperature during the preparation of carbon paper on the microstructure,electrical conductivity,and air permeability of carbon paper,and carbon paper with good performance for fuel cells was successfully prepared.The main conclusions are as follows:(1)Carbon paper produced by different manufacturers has significant differences in carbon fibers and adhesives,which directly affects various aspects of the performance of different carbon papers.The differences in carbon fibers mainly affect the surface density and mechanical properties of carbon paper,while the differences in adhesives mainly affect the electrical conductivity and permeability of carbon paper,and the graphitization temperature of three carbon papers was also analyzed;(2)As the initial fiber surface density increases,the thickness and surface density of the produced carbon paper increase.When the initial surface density of the PAN based nonwoven fabric is 50 g/m~2,the thickness and surface density of the carbon paper prepared are 236.80μm and 73.91 g/m~2,respectively,and the resistivity is 20.76mΩ·cm,which also has good permeability.In the case of the same thickness and surface density,the surface density of MPCF requires 75 g/m~2,and the average thickness of carbon paper is 222μm,therefore,the average surface density and resistivity of it is 101 g/m2,12.66 mΩ·cm,respectively,which is only about 1/2 of the resistivity of carbon paper made by PAN based nonwoven fabrics under the same conditions.(3)Due to the introduction of resin carbon,a good conductive network is formed between the fibers,so as the content of resin carbon increases,the conductivity of carbon paper increases,but the porosity and air permeability decrease.When the content of resin carbon in carbon paper prepared from PAN based nonwoven fabrics is about 25%-35%,the fiber and resin carbon have a good combination,moderate pore number and size,and fewer cracks.When MPCF is impregnated with the same phenolic resin concentration,its performance is best when the resin carbon content is about 25%-30%,and the residual resin carbon content in PAN based nonwoven carbon paper is higher;(4)As the graphitization temperature increases,the resin carbon gradually shrinks towards the fiber surface and the fiber junction,resulting in a gradually larger pore size and higher permeability.At the same time,the microstructure of carbon paper changes from a two-dimensional disordered layer structure to a three-dimensional ordered structure,and the modulus continues to increase,leading to better electrical conductivity,and the mechanical properties firstly increase and then decrease.At the same graphitization temperature,the microcrystalline parameters and graphitization degree of MPCF carbon paper are higher than those of PAN based nonwoven carbon paper,so it also presents a better electrical conductivity.After graphitization at about2000℃,the resistivity of the former is 8.54 mΩ·cm,while the latter is 19.00 mΩ·cm.However,the tensile strength of PAN based nonwoven carbon paper is 42.79 MPa,which is higher than MPCF carbon paper(3.87 MPa). |
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