Preparation Of CNT/Carbon Fiber Composite Carbon Fiber Paper For Gas Diffusion Layers In Fuel Cells

Gas diffusion layers (GDL) is one of key materials for proton exchange membrane fuel cells (PEMFC) and it has several specific functions: reactant permeability, product permeability, electronic conductivity, heat conductivity, mechanical strength. The above functions impose requirements on the chemical and physical properties of GDL. The most promising candidates for GDL are carbon fiber paper or carbon cloth, due to their high porosity and good electrical conductivity. However, carbon fiber paper is monopolized by several foreign companies, like Toray Co. And the domestic research is still in the laboratory stage. In this work, carbon fiber paper was made of carbon fiber and carbon nanotube through wet paper-making method. Effects of the materials and technology on the properties of carbon fiber paper were studied by means of electrical measurement, automatic mercury porosity measurement, micro optical contact angle measurement, SEM and X-ray diffraction. Based on mentioned experiments, the following conclusion can be obtained:Firstly, materials and additives were prepared. Specific process: (a)PAN-carbon fiber with 3-5 mm length; (b)3mol/l NaOH solution was used for activating carbon fiber; (c) dispersant was PEO with 0.01% in pulp water solution; (d) the CNT content of mixture (carbon fiber and CNT) was 8%.Secondly, the above materials and additives were used for making paper. The condition of paper-making was beating time 10 minutes and paper-making time 10 minutes.Thirdly, the carbon fiber paper was used to mold and then it was heat-treated at 2200°C. Molding condition was temperature 145°C, press 4MPa and time 15 minutes.At last, carbon fiber paper was doped entirely in the PTFE solutions and then it was heated at 340°C for 30 minutes.The carbon fiber paper with thickness of 0.3mm, density of 0.4-0.5g/cm~3, resistance of 8-15mΩ·cm, porosity of 75-90%, average pore radius of 20-30jim and contact angle of 120-130°was produced, which basically satisfied the application requirements in PEMFC.