| Summary: | 碩士 === 國立中央大學 === 機械工程研究所 === 93 === Water management is an important issue in order to achieve high performance of proton-exchange membrane (PEM) fuel cell. On the one hand the product water from the chemical reaction needs to be removed in time, or it may block the pores in the catalyst layers as well as the gas diffusion layer (GDL) and then hinders the transport of oxygen and hydrogen, resulting in higher mass transport resistance. On the other hand, water is needed to hydrate the ionically-conducting membrane. So water management and mass transport have been shown to be important factors these strongly influence PEMFC Performance.
The GDL in a PEMFC consists of a micro-porous layer (MPL) of carbon black mixed with polytetrafluoroethylene (PTFE) that is coated onto a sheet of macro-porous carbon backing paper. This GDL not only provides physical micro-porous support for catalyst layer but also provides electrical contact between the electrode and the flow field plate. At the same time, it must allow the water formed on the cathode to exit to the gas channels and permit the passage of water between the gas streams and the membrane surface. Although the GDL is a seemingly minor component in a fuel cell, it has been shown that altering the composition of the diffusion layer can lead to substantial improvements in the performance of the cell.
Though the GDL in a PEMFC plays a critical role in the rise of performance, the GDL remains poorly understood because of a lack interactive effects with the other two main repeating units, the catalyst-coated membrane and the bipolar plate. It is the purpose of the present proposal to conduct a detailed study to investigate the effects of the characteristics of the GDL and MPL, including pore size, pore distribution, hydrophobic and hydrophilic treatment, gas permeability, and AC resistance and capillary force, on the water management and performance of a PEM fuel cell.
In the experiments, we used acetylene-black in MPL. The investigations include the effects of PTFE loading, carbon paper thicknesses and MPL thicknesses. The GDL used are commercial carbon papers: TGPH-060-no proofed, TGPH-090-no proofed, and TGPH-120- no proofed. According to our results, The TGPH-090-no proofed coated with 70μm MPL provides the best water management and performance in the PEMFC. Especially in the middle current density region, we find that when the thickness of MPL is 70μm, the cell has the lowest charge resistance. It also reduces the resistance of mass transport in the high current density region.
|
|---|
