The Proton Exchange Membrane Fuel Cell Developed By Using Carbon Paper

Proton exchange membrane fuel cell (PEMFCs) are attracting considerable interest as alternative power source for automotive, stationary and portable applications due to their high power densities and environmental benefits. Porous conducting carbon paper has been identified as one of the most important components in a fuel cell. It not only acts as an electrolyte and catalyst support, but also allows the diffusion of hydrogen fuel through its fine porosity and serves as a current-carrying conductor and a liquid water-removing channel. Therefore research and development of high quality carbon paper is of great significance to enhance the PEMFC'S efficiency and commercial applications.PAN based carbon fiber paper preform prepared by nonwoven fabrics method was used in this work, and then carbon papers were fabricated by three different ways, that is CVD, molding and molding-CVD complex technology. The structure of the carbon paper was studied and their properties such as graphitization degree, in-plane electrical resistivity, gas permeability and performance of PEMFC were investigated, and the results show that:(1) Carbon papers made by CVD enable carbon fibers have good combination with each other, which enhances the electric transmission and improves the electricity performance. Though the in-plane electrical resistance of the carbon paper after graphitization is in the range of 33.3～34.9mΩ·cm, CVD has limited effect for filling pores in the carbon paper. The thickness of the carbon paper prepared by CVD is 889μm and the density is 0.125g·cm-3, which is lower than the required density that for applications.(2) Modified phenolic resin was used as impregnant in the molding process. The molding pressure and temperature are two key factors that influence the molding process, which have great effects on the thickness, density, permeability and in-plane electrical resistance of the carbon paper. The optimum process to prepare carbon papers with excellent properties is: molding with pressure 4MPa for 1h at temperature 150℃. The thickness of the carbon paper fabricated in this condition is 183μm, with the density being 0.49g-cm-3. The permeability and the in-plane resistivity of the as-prepared carbon paper are 4498ml·mm/cm2·hr·mmAq and 16.9mΩ·cm, respectively.(3) Carbon papers prepared by molding-CVD complex technology reveal a more favorable structure. In this way, pyrocarbon can form continuously and uniformly on the carbon fiber surface, which enhances the combination of carbon fibers and matrix, eliminates the crack flaws, and moreover improves the in-plane electrical resistance. The in-plane electrical resistance of Toray in two directions are 0.42Ωand 0.70Ω, respectively, while the ones of ours are in the range of 0.21～0.45Ωand with less directional diversity.(4) The carbon paper prepared with molding-CVD complex technology exhibit better PEMFC performance than Toray ones in the low gas humidity environment. In the low gas humidity condition (RH60%), with the current density being 0.5 A/cm2, the output voltage of PEMFC corresponding to Toray carbon paper is 0.67V, and the output voltage of ours is 0.7V; with the current density increased to 2.0A/cm2, the output voltage of PEMFC for Toray's is 0.28V, while the output voltage of ours is 0.38V. The density of the carbon paper used in the tests is 0.58 g·cm-3.