Modifications of membrane electrode assemblies to understand and improve water management and performance in PEM fuel cells
Thesis_A._Mohseninia ... (18.99Mb)
PhD dissertation
PhD dissertation
Erstveröffentlichung
2021-04-21Authors
Mohseninia, Arezou
Referee
Tillmetz, WernerStreb, Carsten
Dissertation
Faculties
Fakultät für NaturwissenschaftenInstitutions
Institut für Anorganische Chemie I (Materialien und Katalyse)External cooperations
Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW)Abstract
Polymer electrolyte membrane fuel cells (PEMFCs) have been recognized as a promising zero-emission candidate for automobile applications. Through extensive research and development activities over the last 20 years, PEM fuel cells are now able to start broad commercialization. There is still a large potential to further improve efficiency and durability, where water management is of crucial importance to achieve these advancements. While membrane and ionomer in the catalyst layer should be fully humidified to enable proton conductivity, excessive water accumulation in the porous layers increases the mass transport losses and hence, reducing the cell performance. The present work investigates the influences of microstructural properties of the catalyst layer (CL) and its interactions with the cathode microporous layer (MPLC) on water balance and performance of PEMFCs operating under industrially relevant conditions. By establishing a lab type manufacturing process along with utilizing in situ high-resolution neutron imaging techniques, we studied for the first time the effects of systematic modifications of hydrophobicity and porosity of CLs in combination with the modified cathode MPL materials on water management of PEMFCs. This study helped to deepen the understanding of liquid water transport mechanisms in the porous materials which provides the necessary information for designing and optimizing the structural properties of the engineered materials to improve water management and performance in PEMFCs. Hydrophobicity of the materials was modified using hydrophobic polytetrafluorethylene (PTFE). We found that the operating conditions have a decisive role to define the optimum content of PTFE loading in the layers. While at dry conditions CLs with 5 wt.% PTFE loading enhanced the cell performance by retaining the water in the interface of membrane and CL and thus improving the membrane hydration, CLs with 10 wt.% PTFE improved the performance by decreasing the mass transport losses at humid conditions and high air flow rates. We further investigated the effects and interactions of hydrophobicity gradients within CLs and cathode MPLs on the cell performance and liquid water transport. It was found that the combination of CL with 5 wt.% PTFE and MPLC with 20 wt.% PTFE resulted in the best performance. The analyses of water content showed at humid conditions, higher PTFE loadings (>20%) of MPLC increased the water accumulation in adjacent CL and decreased the transfer of water into the cathode channels, which consequently increased the mass transport resistance at high current i densities. In addition, neutron radiographic studies revealed that water back-diffusion was escalated by increasing the hydrophobicity of the layers. To modify the porosity of CL and MPLC, polymeric pore formers were utilized to create macropores in the structure of materials. The perforated layers enhanced the performance of the cell at both dry and humid conditions, especially at higher current density regions. Neutron imaging analysis revealed different liquid water distributions under land and channel regions. The local water saturation beneath the land regions with the presence of perforated CL and MPLC was increased which is explained by increased water filling of the larger pores due to their lower capillary pressure and also elongated water transport pathways under the land regions. In contrast, under the channels, perforated layers decreased the liquid water content indicating that macropores provided preferential transport pathways to remove the liquid water to the channels. Therefore, the performance improvement is attributed to an enhanced parallel two-phase flow mechanism under channels region where liquid water is transported through the bigger pores, and oxygen is transported through the smaller pores. A maximum performance increase of 30 % at a cell voltage of 0.42 V was achieved for our investigated cell design with the optimized perforated materials.
Date created
2020
Cumulative dissertation containing articles
• A. Mohseninia, M. Eppler, D. Kartouzian, H. Markötter, N. Kardjilov, F. Wilhelm, J. Scholta,
I. Manke, PTFE Content in Catalyst Layers and Microporous Layers: Effect on Performance
and Water Distribution in Polymer Electrolyte Membrane Fuel Cells, J. Electrochem. Soc. 168
(2021) 034509.
https://doi.org/10.1149/1945-7111/abec53
• A. Mohseninia, D. Kartouzian, M. Eppler, P. Langner, H. Markötter, F. Wilhelm, J. Scholta, I. Manke, Influence of Structural Modification of Micro-Porous Layer and Catalyst Layer on Performance and Water Management of PEM Fuel Cells: Hydrophobicity and Porosity, Fuel Cells. 20 (2020) 469–476. https://doi.org/10.1002/fuce.201900203
• A. Mohseninia, D. Kartouzian, R. Schlumberger, H. Markötter, F. Wilhelm, J. Scholta, I. Manke, Enhanced Water Management in PEMFCs: Perforated Catalyst Layer and Microporous Layers. ChemSusChem. 13 (2020) 2931–2934. https://doi.org/10.1002/cssc.202000542
• A. Mohseninia, D. Kartouzian, M. Eppler, P. Langner, H. Markötter, F. Wilhelm, J. Scholta, I. Manke, Influence of Structural Modification of Micro-Porous Layer and Catalyst Layer on Performance and Water Management of PEM Fuel Cells: Hydrophobicity and Porosity, Fuel Cells. 20 (2020) 469–476. https://doi.org/10.1002/fuce.201900203
• A. Mohseninia, D. Kartouzian, R. Schlumberger, H. Markötter, F. Wilhelm, J. Scholta, I. Manke, Enhanced Water Management in PEMFCs: Perforated Catalyst Layer and Microporous Layers. ChemSusChem. 13 (2020) 2931–2934. https://doi.org/10.1002/cssc.202000542
Subject headings
[GND]: Polymer-Elektrolytmembran-Brennstoffzelle[LCSH]: Proton exchange membrane fuel cells
[Free subject headings]: Neutron imaging | Water management | Membrane electrode assembly | PEMFC
[DDC subject group]: DDC 530 / Physics | DDC 600 / Technology (Applied sciences)
Metadata
Show full item recordDOI & citation
Please use this identifier to cite or link to this item: http://dx.doi.org/10.18725/OPARU-36770
Mohseninia, Arezou (2021): Modifications of membrane electrode assemblies to understand and improve water management and performance in PEM fuel cells. Open Access Repositorium der Universität Ulm und Technischen Hochschule Ulm. Dissertation. http://dx.doi.org/10.18725/OPARU-36770
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