Morphological and electrochemical investigation of polymer electrolyte fuel cell components

Hochschulschrift

Abstract: In this thesis devices for electrochemical energy conversion and storage are investigated with tomographic and electrochemical methods with a focus on polymer electrolyte fuel cells. The first part of the work presents ZnO-contrasting via atomic layer deposition for focused ion beam - scanning electron microscopy (FIB-SEM) tomography, which for the first time enables reliable and fast reconstruction of nanoporous carbon-based materials. The potential of ZnO-contrasted FIB-SEM tomography is illustrated with various findings: the calculated O2 diffusivities (23.1 - 25.4 x 10-7 m2s-1) and porosity (65%) of a fuel cell catalyst layer are in good agreement with experimental values from literature, while they deviate strongly when obtained from state-of-the-art reconstructions. Furthermore, filling with ZnO permits the identification of large Pt clusters inside the catalyst layer, which were estimated to reduce the catalyst surface area by 9%. A similar material system, the carbon binder domain (CBD) of a LiCoO2 battery cathode, was reconstructed for the first time thanks to ZnO-contrasting possibly ending the era of virtually created CBDs via stochastic-based reconstruction. The calculated porosity (57%), tortuosities and size distributions lead to two findings: first, the inhomogeneity of the CBD reduces electronic conductivity by up to 30%, and second, swelling of the PVDF binder (75 vol%) reduces ion transport in the pores of the CBD significantly. ZnO-contrasting is further used to compare a fuel cell microporous layer and catalyst layer, to demonstrate the pore space connectivity of carbon nanowalls synthesized by plasma enhanced chemical vapor deposition and to investigate the morphology of supercapacitor materials. Most likely ZnO-infiltration also aids to preserve the original structure of the sample during FIB-SEM tomography by increasing mechanical stability and thermal conductivity. Being the missing piece to reliably reconstruct large volumes ZnO-contrasting is believed to pave the way for industrial application of FIB-SEM nanotomography.
In the second part of the thesis the reasons for the increased power density of fuel cells fabricated with the in-house developed direct membrane deposition (DMD) are systematically investigated. The reasons for the increased power density were found to be a 50% reduction in ionic resistances of the polymer electrolyte membrane and mass transport resistance of the oxygen diffusion compared to conventional fuel cells. The reduced mass transport losses, which are responsible for 90% of the increase in power density (at the maximum power point of the reference), are attributed to an increased cathode water removal through the membrane due to a thinner membrane, differences in catalyst layer morphology and an increased membrane surface

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: IN COPYRIGHT http://rightsstatements.org/page/InC/1.0 rs ; Albert-Ludwigs-Universität Freiburg, Dissertation, 2016

Klassifikation und Themen

• Klassifikation: Elektrotechnik, Elektronik
• Schlagwort: Polymer-Elektrolytmembran-Brennstoffzelle ; Lithium-Ionen-Akkumulator

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2016
• Urheber: Vierrath, Severin
• Beteiligte Personen und Organisationen: Zengerle, Roland ; Albert-Ludwigs-Universität Freiburg. Professur für Anwendungsentwicklung ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften ; Albert-Ludwigs-Universität Freiburg

Weitere Informationen

• DOI: 10.6094/UNIFR/12696
• URN: urn:nbn:de:bsz:25-freidok-126966
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:44 MEZ