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Book/Dissertation / PhD Thesis | FZJ-2022-01250 |
2021
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-606-9
Please use a persistent id in citations: http://hdl.handle.net/2128/30879 urn:nbn:de:0001-2022040529
Abstract: To make fuel cells accessible to a broader application, cost reduction is necessary. An important component of the fuel cell with great cost reduction potential is the bipolar plate. At the same time, the quality of the bipolar plate is of decisive importance for the function of a fuel cell and its longevity. New test methods are needed for the quality assurance of the bipolar plate. In this work, a method and a test setup based on the propagation of the electric potential field is developed for the detection of defects in graphite composite bipolar plates and bipolar plate materials. A current is passed through the bipolar plate via a point contact. With measuring points around the contacting point, the potential field in the bipolar plate can be recorded and analyzed for disturbances. Central elements of the test setup are two probes with 25 spring-loaded measuring tips, which are moved over the bipolar plate. Depending on the programming, the measuring tips conduct a current through the sample or measure the potential field forming in the sample. X-ray tomography and electrical potential simulations are used as a reference and to evaluate the measurement results of the test setup. The measurement method is tested and potential measurement uncertainties are identified on material strips of blank plates with through holes as defined artificial defects. A complex electrical conductivity network is formed in the graphite composite bipolar plates by the graphite particles. The conductivity network becomes visible as measurement noise in the results of the potential field measurements. The application of the measurement method to bipolar plates is demonstrated on monopolar plates withone-sided flow field, in which artificial defects are imitated by plastic accumulations, admixed wood and steel particles. The plastic accumulations represent non-conductive regions in the bipolar plate and the wood particles represent isolated defects such as cracks, voids or non-conductive foreign bodies. Massive defects such as plastic accumulations can be identified with the test setup and their local manifestations determined. Isolated defects, on the other hand, are not detected with the test setup. Ohmic resistance measurements on the monopolar plates and cutouts from the monopolar plates prove that only large-scale defects have a negative influence on the electrical conductivity of bipolar plates. Fuel cell tests with the monopolar plates confirm the results of the ohmic resistance measurements, according to which isolated defects have no influence on ohmic resistance and fuel cell performance. The developed test set-up is suitable for random measurement of electrical properties and detection of performance-impairing defects in bipolar plates.
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