Preprint of Interaction phenomena of automotive PEM fuel cell stacks during error states of reactant starvation

Preliminary excerpts from dissertation for the award of the doctoral degree Title: Interaction phenomena of automotive PEM fuel cell stacks during error states of reactant starvation Doctoral candidate: Jens Thomas Nissen (https://orcid.org/0000-0002-1655-4644) University: Ulm University Faculty: Fakultät für Naturwissenschaften Institute: Zentrum für Sonnenenergieund Wasserstoffforschung (ZSW) Ulm Supervisor: Prof. Dr. Markus Hölzle Industry cooperation with: cellcentric GmbH & Co. KG Company supervisor: Dr. Jan Nicolas Schwämmlein Last Update: 08 November 2024 Confidentiality: Public preliminary version Digital Object Identifier (most up-to-date version): 10.5281/zenodo.14012924 Intended publication of final version: Spring 2025 Licensing: This document is licensed under CC-BY 4.0, see https://creativecommons.org/licenses/by/4.0/legalcode.en Unit cell geometry Figure 1: Photo of the carbon composite bipolar plate with the anode flow field facing upwards. Copyright by CELLCENTRIC GMBH & CO. KG, reproduced with permission. Source: https://www.youtube.com/watch?v=MyO-r-nrrrU&t=84s Pneumatic compression hardware Figure 2: Photo of the pneumatic compression hardware, containing a 20-cell fuel cell stack. Local cell voltage distribution measurement Figure 3: Experimental setup of the local voltage distribution measurement for cell #1 in a 20-cell stack. Subfigures depict a) a single cell voltage pickup, b) assembly of 18 cell voltage pickups and the framed membrane electrode assembly (gas diffusion layer replaced by dark grey rectangle, frame replaced by light grey shape due to non-disclosure), c) two assemblies of cell voltage pickup and framed membrane electrode assembly as cell #1 and cell #2 in a 20-cell short stack, mounted in the pneumatic compression hardware. Figure 3 shows photos of the experimental setup of the local voltage distribution measurement. Figure 3a shows one of the self-crafted cell voltage pickups. These pickups were cut out from a gold coated stainless steel sheet. The tip of those pickups was narrowed down and the sheet was bent slightly so that it may adjust its height elastically in the finally assembled state. The pickups were folded two times into a Z-shape so that they sticked better and kept in their intended positioning in the following manufacturing step. A wire was soldered to each pickup for electrical connection. Figure 3b shows how these pickups were connected to the framed membrane electrode assembly. 18 cell voltage pickups were hereby taped onto an additional transparent foil in the desired positions. The tips of the pickups hereby slightly reached over the edge of the transparent foil and faced upwards. This foil was then taped from the bottom side to the framed membrane electrode assembly. The bottom side of the cell voltage pickups thus contacted the electrically isolating frame, while the non-isolated gold coated tips faced upwards. Figure 3c shows how two of those modified framed membrane electrode assemblies were mounted as cell #1 and cell #2 in a 20-cell stack, which was compressed in the pneumatic compression hardware (compare figure 2). The gold coated top side of the cell voltage pickup tips hereby elastically touched the flow field plate above the respective cell to ensure proper electrical contact. The cables of these pickups were then connected to an additional SMART TESTSOLUTIONS G5 cell voltage monitoring unit. This unit therefore measured the voltage of cell #1 as the difference in electric potential from the bottom site of the anode interface plate to the bottom side of bipolar plate #1 at all 18 electrical tap points along the media flow direction. The electrical tap points of this local voltage distribution measurement were consequently located at the bottom side of the flow field plates and at their long edge. This position differed from the simultaneously performed 2-fold multi-point cell voltage monitoring measurement, which contacted the flow field plates at the short edge beyond the media ports and at half thickness of the plate. The third presented publication inspects the agreement between these two measurement techniques in more detail.