| Summary: | 博士 === 國立中央大學 === 機械工程研究所 === 100 === First, the experimental results of the PEM fuel cell with metal foam as flow distributor will be reported. These experimental results show the characteristics of the PEM fuel cell with the metal foam as flow distributor and extend our understanding of the relation between cell performance and mass transport properties into a region of parameters that the conventional PEM unit cell can not provide. The comparison in polarization curve is made between the PEM unit cell with different metal-foam properties and the PEM unit cell with graphite flow channel plate as flow distributor. The experimental results show that the PEM fuel cell with metal foam as flow distributor possesses some unique characteristics compared with the conventional PEM unit cell with flow channel plate as flow distributor.
Due to the high porosity of metal-foam (over 80 %) plus convective flow through the metal-foam, mass transport limitation phenomenon is not as pronounced as in the case of conventional PEM unit cell with flow channel plate as flow distributor. Another interesting phenomenon is that electrical conductivity of metal-foam plays a significant role in performance, which is seldom the case in the conventional PEM unit cell with flow channel plate as flow distributor. Although there are several technical challenges to be overcome for the current form of metal-foam to replace flow channel plates, the unique mass-transport properties of metal foam plus its light weight are very attractive.
In the second part, the improvements made on the PEM fuel cell with metal foam as the flow distributor are reported. The comparison in polarization curve is made between the PEM unit cell with different metal foam flow field designs and the PEM unit cell with graphite bipolar plate as flow distributor. The experimental results show that after using improved metal foam flow field designs, the fuel cell’s performance increases. Because the gas flow is limited by the flow inlet and the metal foam geometry, different flow field design will affect the flow pattern.
the results show that, in the PEM unit cell with single zone metal foam, convection is weak at side corners. Dividing the metal foam into multiple regions and using multiple inlets effectively increases the gas distribution. AC impedance measurement was also performed to study the impedance characteristics. The Nyquist and Bode plots confirmed that Ohmic resistance, activation resistance, and mass transfer resistance of metal foam fuel cell are all smaller than that of conventional PEM unit cell.
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