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Sub-second dynamics of liquid water transport in polymer electrolyte fuel cells revealed by 4D X-ray Tomographic Microscopy

English title Sub-second dynamics of liquid water transport in polymer electrolyte fuel cells revealed by 4D X-ray Tomographic Microscopy
Applicant Büchi Felix
Number 166064
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Physical Chemistry
Start/End 01.11.2016 - 30.11.2020
Approved amount 586'628.00
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All Disciplines (2)

Discipline
Physical Chemistry
Fluid Dynamics

Keywords (5)

Polymer Electrolyte Fuel Cells; Ultra-fast X-ray Tomographic Microscopy; Water Management; Low Signal-to-Noise Image Evaluation; Dynamics of Liquid Water in Porous Materials

Lay Summary (German)

Lead
Titel des Forschungsprojekts Ultra-schnelle Röntgenmikrotomographie des Wassertransportes in Brennstoffzellen?Microscopie tomographique rayon X ultra-rapide du transport de l’eau dans les piles-à-combustiblesUltra-fast X-ray tomographic microscopy of water dynamics in fuel cellsLead Der Verkehr war 2014 in der Schweiz für die Emission von über 40% des Treibhausgases CO2 verantwortlich. Brennstoffzellen mit erneuerbarem Wasserstoff als Treibstoff sind eine saubere Technologie welche ein bedeutendes Potenzial zur Reduktion der CO2-Emissionen des Verkehrs aufweist. Die Brennstoffzellentechnologie ist heute jedoch für den verbreiteten Einsatz noch zu teuer. Kostenreduktion kann einerseits durch die Verwendung billigerer Materialien und Herstellungsprozesse oder andererseits durch Erhöhung der Leistungsdichte erreicht werden.
Lay summary

Inhalt und Ziel des Forschungsprojekts

Unser übergeordnetes Ziel ist, zu einer Erhöhung der Leistungsdichte von Brennstoffzellen für mobile Anwendungen beizutragen. Es ist gut bekannt, dass die Verbesserung der Leistung durch das Verweilen des Reaktionsproduktes Wasser in den mikroskopischen Poren der Zellen beeinträchtigt wird. Zum besseren Verständnis dieses Problems entwickeln wir (i) eine 100 x schnellere Röntgen-Mikrotomographie Methode (10 3D-Bilder pro Sekunde) an der Swiss Light Source zur Abbildung des flüssigen Wasser im Innern der Brennstoffzelle in 3D (ii) eine 3D-Bildauswertung von stark verrauschten Daten und (iii) erarbeiten das Verständnis der Bewegung des flüssigen Wassers in der Zelle.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts

Unsere Arbeit wird neue und wichtige Informationen über das Verhalten des flüssigen Wassers in Brennstoffzellen generieren. Die Ergebnisse werden die Entwicklung von Materialien mit höherer Leistung ermöglichen, so dass die Kosten der Brennstoffzellen-Technologie sinken und das Projekt so einen Beitrag zur grösseren Verbreitung der nachhaltigeren Fahrzeuge leistet. Die Entwicklungen der Röntgentomographie können auch von vielen anderen wissenschaftlichen Fragestellungen genutzt werden. 

Direct link to Lay Summary Last update: 15.04.2016

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
153790 Designing multifunctional materials for proton exchange membrane fuel cells 01.10.2014 NRP 70 Energy Turnaround
180335 Pushing PEM Fuel Cells to Their Full Potential: Materials Development and Porous Layer Design Guided by Advanced Diagnostics 01.11.2018 Sinergia
183297 A modular sample manipulator for dynamic tomography under real conditions 01.01.2019 R'EQUIP
169913 Coupled multi-phase transport in porous layers for fuel cells utilizing evaporative cooling 01.02.2017 Project funding (Div. I-III)

Abstract

Hydrogen fed polymer electrolyte fuel cells (PEFC) are expected to play a major role in a future decarbonized energy system, in particular in the mobility sector. Water management is the major limiting factor in PEFC for further increasing power density. Therefore the aim of this project is to improve performance, but also stability and durability of PEFC by unraveling the dynamics of liquid water in the porous gas diffusion layers (GDL) of PEFC. The project will scientifically develop around two PhD theses hosted at PSI in the Electrochemistry Laboratory and the X-ray tomography group (also responsible for the TOMCAT beamline). The project aims at the development of sub-second tomographic imaging of PEFC for visualizing and ultimately understanding the liquid water dynamics in the GDL, which today limits performance. In vehicles and other demanding applications the fuel cell is operated in non-steady state mode, following a transient load profile. This requires a fast characterization technique for understanding of the transient water transport in the GDL. Operando X-ray tomographic imaging (XTM) is a powerful technique able to image the liquid water in PEFCs on the scale of GDL pores with pixel sizes of 2 to 3 micrometers. However, today the fastest operando XTM scans require acquisition times of about 10 s, limiting the technique to investigation of stationary operation conditions and fail to deliver insight into fast snap-off and Haines-jumps dynamics of the liquid phase that are expected to dominate during transient PEFC operation. Further, due to the radiation sensitivity of PEFC, with present imaging conditions only a low number to 3 - 4 tomograms can be acquired without radiation bias, which limits insight, as increased statistics over several cell set-ups are required.The project intends to reduce scanning time by two orders of magnitude vs. state of the art to 0.1s for a 3D-volume. This requires the development of advanced imaging procedures, improving the signal to noise ratio at short scanning times and data post-processing approaches that allow to identify the liquid water phase in the 3D-images from low signal to noise CT data. Further an upgrade of the beamline optics is necessary, where the installation of a new microscope with a high numerical aperture lens (NA of >= 0.35) is planned. With the increased number of scans, the redistribution of the water phase over various timescales will be accessible, enabling an ultimative understanding of the coupling of power limitations at transient PEFC operation with liquid water dynamics at the pore scale level. The new insights will clarify the controversy whether capillary pressure driven liquid flow or root like merging of various independent condensation clusters are the major mechanism of water transport in the GDL. Further the temporal build up of liquid water paths after significant changes of the current density of the cell, understanding of the voltage fluctuations under high humidity operation conditions, as well as the temporary power loss after a fast increase of power density will be understood. Results will provide important input for the GDL structural development allowing for better effective gas phase transport under high current density conditions, enabling higher PEFC power density.
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