Research On Preparation And Properties Of Carbon Fiber Paper With Gradient Structure

Carbon fiber paper(CP)is widely used as the base material for the gas diffusion layer of proton exchange membrane fuel cell.It undertakes the transmission of gas,liquid,electricity and heat,which is one of the significant materials for fuel cell.The structure and properties of CP directly affect the performance of the fuel cell.Aiming at the highperformance requirements of high-capacity fuel cells for CP such as high conductivity,high air permeability and support strength,along with the outstanding problem of between air permeability and mechanical properties at present,this paper uses domestic carbon fibers(CFs)as raw materials to carry out wet forming technology to prepare CP with gradient structure for gas diffusion layer.The study systematically explored effects of chopped CFs modification,dispersant,and dispersion mass fraction on the dispersion uniformity of CFs,and the effects of various process conditions for preparing CP on the structure and properties of CP.On this basis,a novel process for preparing CP body was developed by impregnating carbon black modified phenolic resin,using domestic carbon fiber felt.After hot-press,carbonizing and graphitization,CP with gradient structure was obtained by various areal densities,with conductivity and mechanical behavior improved.The main results are as follows:(1)The optimal dispersion conditions of short-chopped CFs in aqueous solution were obtained: 0.04 wt% polyethylene oxide aqueous solution with 0.4 wt% CFs.Carbon fiber felts with different areal densities were prepared by wet forming.The precursor is then subjected to doublelayer and multi-layer by overlay-forming,resin impregnation,carbonization,and graphitization to obtain CP with gradient structure.The analysis results show that the graphitization degree of carbon paper reaches 93.14%,the average porosity of multi-layer carbon paper is 75.5%,and the average porosity of double-layer CP is 81.4%.The air permeability of the multi-layer CP is 5272 m/(k Pa·h),the in-plane resistivity is 11.78 mΩ·cm,and the tensile strength and flexural strength are 20.6 MPa and 60.9 MPa,respectively,all better than those of commercial CP.In addition,the gradient CP exhibited better corrosion resistance than commercial CP in acidic media.(2)Using domestic carbon fiber felt as raw material,conductive carbon black(CCB)modified phenolic resin ethanol solution which was obtained by in-situ synthesis as impregnation solution,varying the concentration of CCB.Carbon fiber base paper with different areal densities was obtained by impregnating and then overlayed according to vertical gradient of areal density.CP with gradient structure was obtained by hot pressing,carbonization and graphitization heat treatment.The result shows that the graphitization degree of the bilayer gradient CP with 0.2 wt% of CCB of lower layer is 69.07%,the resistivity is 4.77 mΩ·cm,the porosity is 77.5%,the air permeability is 2999 m/(k Pa·h),the tensile strength and flexural strength are 45.2 MPa and 88.4 MPa,respectively.