Studies On Fabrication Of Micro-Porous Layer In PEMFC

To improve the specific power of PEMFC for transportation is one of the most important targets for R&D of PEMFC. One of the key issues is to decrease the mass transport limitation, which is caused by the lack of reactant gases at the reaction sites, especially when PEMFC is operated at higher current density. Mass transport of the reactant gases will be serious affected by the liquid water inside of cell.The two phase flow of water and gas in Gas diffusion layer (GDL) is influenced significantly by the structure and properties of GDL. The introducing of micro-porous layer (MPL) has been proved to be an effective way to improve the mass transport due to its ability of"water management". While the structure and properties of MPL and GDL are influenced by the fabrication process of MPL. To study and fabricate the GDL with proper porous structure and to enhance the transport of gas and liquid water are very important for improving PEMFC output performance.In this thesis, the preparation of MPL by using dry-layer deposition was conducted. And the comparative investigations on dry-layer MPL and wet-layer MPL were performed by applying SEM, BET, mercury porosimetry and single cell measurements.The main conclusions are as follows:The performance of PEMFC single cell, especially the performance at higher current densities is improved obviously by introducing MPL. The cell based on dry-layer MPL showed superior performance to that based on wet-layer MPL. The formation process of dry-layer MPL and wet-layer MPL is quite different. The pore structure of support layer (water-proofed carbon paper) was modified in the different way depending on the preparation method of MPL. The amount of micro-pores in GDL is increased obviously by adding MPL, and the ratio of super macro-pores (pore size larger than 15　m) is decreased due to the filling up of the larger pores of support layer by MPL. At meanwhile the amount of meso-pores and macro-pores is increased due to the modification of pore structure of support layer by fabricating MPL. The amount of meso-pores and macro-pores in GDL based on dry-layer MPL is the largest one among GDLs based on wet-layer MPL and without MPL and the cell based on dry-layer MPL showed the best performance. It can be concluded that meso-pores and macro-pores are very crucial for gas transport when the super-macro pores are filled by liquid water.Moreover, the GDL based on dry-layer MPL exhibited more excellent electronic conductivity and stable hydrophobicity than that based on wet-layer-MPL. The reproducibility of dry-layer deposition of MPL is also satisfied.