Research of Thin Gas Diffusion Layer Manufacturing Process for Proton Exchange Membrane Fuel Cells

• Main Authors: Cheng-Hao Ciou, 邱承浩
• Other Authors: 楊錫杭
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/9wd7s2

碩士 === 國立中興大學 === 精密工程學系所 === 99 === Ultrathin gas diffusion layer (GDL) can significantly reduce the hydrogen fuel cell stack size. This research aims to study the ultrathin carbon fiber paper fabrication for proton exchange membrane fuel cells (PEMFCs). Polyacrylonitrile (PAN) based carbon fibers with 6 mm long was dispersed and formed at the basis weights of 15g/m2 and 20 g/m2 by a slurry molding machine. The disperse agent polyscrylamide (PAM) and polyvinyl alcohol (PVA) solutions for fiber binding were added to help carbon fibers distribution evenly and increase the paper mechanical strength. The 28x28 cm2 carbon fiber papers were completed. Since heat treatment is required to reduce carbon fiber paper electrical resistance, the phenolic resin plays the fiber binding purpose. It’s a thermosetting resin containing carbon after pyrolysis. The phenolic resin was diluted to 16 to 33% for carbon fiber papers impregnation. After impregnation, the carbon fiber papers were dried by a convective oven at temperature 120℃ for 10 minutes. After impregnating the fiber papers with different concentrations of phenolic resin, a hot press process can set down the fiber paper to the desired thickness. The hot press machine was heat to temperature160℃ and press the workpieces for 10 minutes. Two heat treatment steps were used. Low temperature heat treatment (raise the temperature to 850℃) was to carbonize the phenolic resin and bond the carbon fibers. High temperature treatment (raise the temperature to 1650℃) was to graphitize the carbon fiber and related carbon structures. After graphitization, gas diffusion substrates (GDS) in the paper form are finished. GDS then be immersed to the 5% polytetrafluoroethylene (PTFE) solution and coated with a micro porous layer (MPL), the ultrathin GDL is completed. The experimental results of this ultrathin GDLs include the thinnest thickness 48 μm, tensile strength 32~39N/cm, electrics resistance 2.5mΩ‧cm2, and gas permeability 750 cm3/cm2/s. In the Tafel test, when the cell voltage is 0.6 V, hydrogen and air gas flow ratio is 1.5/2.5, and the working temperature is 60 ℃, without the back pressure, the maximum current density is 815mA/cm2. This study shows the ultrathin GDL fabrication suitable for PEMFC applications and exhibits the feasible functionality for fuel cells.