Studies On Membrane Electrode Assembly Of Proton Exchange Membrane Fuel Cells

Membrane electrode assembly (MEA) is one of the key components of proton exchange membrane fuel cells (PEMFCs). The electrode, composed of the catalyst layer (CL) and the gas diffusion layer (GDL), plays an important role in the mass transportation and electrochemical reactions. The research and development of MEA with reasonable structure and properties not only determine the performance of PEMFC, but also effect on reducing the cost, improving the power density and accelerating the commercialization.A novel Nafion-pyrolyzed electrode was developed based on the advantages of both PTFE-bonded electrode and Nafion-bonded electrode. In such an electrode, Nafion serves as bonders and proton conductors and the prolyzed Nafion without sulfonic acid group acts as hydrophobic materials. The three-phase reaction zones are extended and the utilization of catalysts is increased to some extent. As a result, the improved cell performance was obtained.Based on the research of mass transportation in the substrate layer, the importance of the micro-porous layer (MPL) was proved by its excellent ability in gas/water management. The influence of carbon black on MPL pore structure was examined. It was found that the carbon black with proper specific surface area and pore volume was necessary for the construction of MPL. With the micro-pore-blocking treatment, a carbon black with larger surface area and higherpore volume was modified. Much progressive cell performance was obtained by the MPL using the modified carbon black compared with the original carbon black.A novel bi-functional MPL with composite carbon black consisting of 20 wt% Black Pearls 2000 carbon and 80 wt% Acetylene Black carbon was suggested for the first time and exhibited optimal hydrophilic/hydrophobic porosity. Furthermore, a GDL with a gradient in porosity by adding MPLs with different carbon loading on the catalyst layer side and on the flow field side was proposed.Intermittent microwave irradiation method was successfully used to synthesize composite powders of PTFE supported on carbon black (PTFE/C) which was employed to prepare MPLs. The results showed that the MPL with the as-prepared hydrophobic carbon particles could enhance the mass transportation and improve the cell performance. Also, the process of MPL preparation is simplified by the adoption of PTFE/C and the good reproducibility is guaranteed, which is more suitable to use in practice.