In this thesis the experimental method is used to study the characteristics of a DMFC when a heterogeneous carbon fiber bipolar plate is applied to it. The first main study is about the effect of the different structures of the carbon fiber bunch on the fuel cell performance. Additionally, a high temperature hot-pressing process is performed to change the inner molecular structure so that the hydrogen ion can be blocked to avoid the lateral migration between two adjacent cells. Finally, the two techniques are applied to make our new portable DMFC stack.
The bipolar plates with the sawtooth or non-sawtooth carbon fiber bunches have been used in making our DMFC stack. The experimental results display that the performances of the two structures both are better than the traditional graphite bipolar plate. However, the performance of DMFC with the sawtooth bipolar plate is much better than that without sawtooth, especially in high current density. When carbon fiber bunches with sawtooth use at anode and cathode of bipolar plates, the performance can be enhanced and its power density 27.6% higher than that without sawtooth.
During our study we also found that part of hydrogen ions can laterally migrate to its adjacent cathode and do not directly cross to its opposite cathode, when the banded type MEA are used to multiple cell stack. Therefore, the performance cannot be performed well due to this type ion transfer. In order to block the lateral migration, the narrow area of the membrane between two adjacent electrodes is pressed with a high temperature hot-pressing device. After a short time hot-press between two adjacent electrodes, the hydrogenion migration phenomenon reduced, and the performance had been improved about 10% higher than that without hot-press.
Finally, a double layer 2x6-cell flat type DMFC is made. This 12-cell stack is composed of each electrode area 0.5x5cm2, two sheets of membrane for 6-cell using Nafion 117, the anode catalyst Pt-Ru loading 4mg/cm2, and cathode catalyst Pt loading 4mg/cm2, the methanol concentration 3M, air-breathing, and operating in room temperature. The output power of the cell can reach an average power density 8.0mW/cm2 and total power 240mW with our handmade stack. If the performance of each fuel cell is more uniform, we expect that total power can reach 480 mW. The power level should be satisfied for any kind mobile phone.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0824106-152115 |
| Date | 24 August 2006 |
| Creators | Wang, Yung-Bin |
| Contributors | none, none, none |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0824106-152115 |
| Rights | not_available, Copyright information available at source archive |
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