Home > Publications database > Eignung von nickelhaltigen Katalysatorsystemen in sauren Medien zur Nutzung im Betrieb von Brennstoffzellen |
Book/Dissertation / PhD Thesis | FZJ-2022-05281 |
2022
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-663-2
Please use a persistent id in citations: http://hdl.handle.net/2128/33227 urn:nbn:de:0001-2023013169
Abstract: Catalysts for the oxygen reduction reaction in fuel cells are more favorable when platinum is replaced by alternative materials such as non-precious metals and their catalytic activity is increased. This work addresses a reduction of platinum in the cathode of a direct methanol fuel cell by using nickel. Two approaches are investigated: platinum-nickel alloys and core-shell structures. Automated ultrasonic spraycoating was used to produce mechanically stable electrodes with reproducible electrochemical properties. In addition, whole catalyst-coated membranes (CCMs) were integrally fabricated using ultrasonic spray technology. The ionomer to carbon ratio (I/C) in the electrode was shown to have a significant effect on the electrochemically active surface area (44.7 (I/C 0.87) and 53.0 m2 g-1 (I/C 0.5)). Core-shell catalysts have lower powerdensities than the alloys. Long-term stability of at least 1000 hours of operation with increase in performance is given for both. Both catalyst types experience significant nickel discharge from the surface of the particles, which explains the performance increases. Both alloy and core-shell catalysts exhibit increased methanol tolerance compared to commercial platinum particles. In addition, fabrication of membraneelectrode assemblies has been demonstrated as an integral process by ultrasonic spraying of the electrode and membrane. Thermal modification could be used toimprove the conductivity of the membranes but is not practical in real processes and results in performance losses under the selected conditions. Modification of the membranes with high-boiling solvents also does not result in any improvements. Trace amounts or degradation products of the solvents (DMAc, DMF) lead to membrane poisoning and higher ionic resistivities (0.18 untreated, 0.30 with DMAc and 2.18 Ω cm2 with DMF). Membranes with very good protonic conductivity and low permeations are obtained using graphene oxide as an additive. Thin membranes (20 30 μm) with graphene oxide have up to 20% better protonic conductivity and 50% lower hydrogen permeation. However, the methanol permeation does not decrease. In the long term, the results and findings obtained in this work can lead to a significant reduction in theplatinum content in fuel cells, a simplification of the manufacturing process and an improvement in the properties in terms of permeation, performance, and stability of the membrane-electrode assemblies
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