| Summary: | 碩士 === 國立勤益科技大學 === 機械工程系 === 98 === Nowadays, ultra fine channels and ribs cannot be formed on the commonly used graphite bipolar plates owing to low strength and brittleness of the graphite material. Therefore, this study used the stainless steel plate, SUS316L, with 1mm thick stainless, as the material of the bipolar plates, and these metallic bipolar plates are with reaction area of 20mm×20mm, height and depth of 0.8mm and ribs widths of 0.2mm, 0.4mm and 0.6mm respectively (open area rate of 85.36％, 70.24％, 58.19％,respectively). These formed metallic bipolar plates were assembled with MEA and subsequent cell performance experiments were performed to discussed the affections between the dimensions of the ribs and the channels and the performance of the proton exchange membrane fuel cell (PEMFC).
The experimental results show that the metallic bipolar plate with ribs width of 0.4 mm has the optimum cell performance. The current density of the fuel cell with the metallic bipolar plate with rib width of 0.4 mm was 34.21% higher than the current density of the fuel cell with the metallic bipolar plate with rib width of 0.6mm while the voltage was 0.499V. Although, the metallic bipolar plate with 0.2mm rib width comprising the largest reaction area between fuel and MEA, the excessive open area rate reduced the effective electron transmitting, and increased internal resistance. Therefore, the performance of the metallic bipolar plate with 0.2 mm rib width is lower than the one with 0.4 mm rib width. On the other hand, the flow rate of the gas also affects the performance of the cells. When the flow rate of the gas was set at 60cc/min, better cell performances were found in all of the three cells with different rib and channel dimensions of the metallic bipolar plates. There were no significant performance differences between these three fuel cells when the flow rate of the gas was increased to 80cc/min because sufficient fuel was supplied for reaction when the flow rate was at 60cc/min. When the flow rate of the gas was set at 40cc/min, concentration polarization occurred in the fuel cells with bipolar plates with 0.6 and 0.4 mm ribs width owing to the short channel length with insufficient fuel flow. Better performance was found in the fuel cell with bipolar plate with 0.2mm rib width because of the longer length of the channel and the sufficient time for reaction.
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