ORCID Profile
0000-0002-9348-984X
Current Organisation
Paul Scherrer Institut
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Publisher: American Chemical Society (ACS)
Date: 16-03-2021
Publisher: The Electrochemical Society
Date: 2012
DOI: 10.1149/2.042208JES
Publisher: The Electrochemical Society
Date: 2018
DOI: 10.1149/2.0831809JES
Publisher: The Electrochemical Society
Date: 11-2021
Abstract: Understanding the water dynamics during the sub-zero operation of polymer electrolyte fuel cells can help to optimize the materials and operating strategies to achieve successful freeze starts. This study employs sub-second X-ray tomographic microscopy to study the effect of downstream flow conditions on the water distributions during dynamic freeze starts from −30 °C by varying the feed gas humidity. An increase in the feed gas humidity resulted in a decrease in electrochemical performance. To probe the catalyst layer (CL)-micro-porous layer (MPL) interface, a MPL with grooves across it’s entire thickness was used. Imaging results showed that during the initial phase of performance drop due to ice formation, all the water produced was limited to the CL and membrane. The total water observed during the sub-zero operation in the MPL grooves was 1–2 orders of magnitude lower than the theoretical water produced and increased with an increase in the gas RH from 0% to 50% but reduced with further increase to 100% RH due to a lower cell performance. The overall saturation in the GDL was zero during the sub-zero operation and increased to less than 1% above 0 °C indicating minimal effect of the GDL mass transport on the freeze start performance.
Publisher: Elsevier BV
Date: 03-2021
Publisher: MDPI AG
Date: 20-05-2021
DOI: 10.3390/EN14102967
Abstract: Facilitating the proper handling of water is one of the main challenges to overcome when trying to improve fuel cell performance. Specifically, enhanced removal of liquid water from the porous gas diffusion layers (GDLs) holds a lot of potential, but has proven to be non-trivial. A main contributor to this removal process is the gaseous transport of water following evaporation inside the GDL or catalyst layer domain. Vapor transport is desired over liquid removal, as the liquid water takes up pore space otherwise available for reactant gas supply to the catalytically active sites and opens up the possibility to remove the waste heat of the cell by evaporative cooling concepts. To better understand evaporative water removal from fuel cells and facilitate the evaporative cooling concept developed at the Paul Scherrer Institute, the effect of gas speed (0.5–10 m/s), temperature (30–60 °C), and evaporation domain (0.8–10 mm) on the evaporation rate of water from a GDL (TGP-H-120, 10 wt% PTFE) has been investigated using an ex situ approach, combined with X-ray tomographic microscopy. An along-the-channel model showed good agreement with the measured values and was used to extrapolate the differential approach to larger domains and to investigate parameter variations that were not covered experimentally.
Publisher: International Union of Crystallography (IUCr)
Date: 02-11-2013
DOI: 10.1107/S1600577513025162
Abstract: The degradation of cell performance of polymer electrolyte fuel cells under monochromatic X-ray irradiation at 13.5 keV was studied in galvanostatic and potentiostatic operation modes in a through-plane imaging direction over a range of two orders of magnitude beam intensity at the TOMCAT beamline of the Swiss Light Source. The performance degradation was found to be a function of X-ray dose and independent of beam intensity, whereas the degradation rate correlates with beam intensity. The cell performance was more sensitive to X-ray irradiation at higher temperature and gas feed humidity. High-frequency resistance measurements and the analysis of product water allow conclusions to be drawn on the dominating degradation processes, namely change of hydrophobicity of the electrode and sulfate contamination of the electrocatalyst.
Publisher: The Electrochemical Society
Date: 10-2022
Abstract: Desaturation of polymer electrolyte fuel cells (PEFCs) is a critical operation step for providing cell cold-start performance by minimizing residual water in the gas diffusion layers (GDLs), flow field (FF) channels, catalyst layers and membrane after cell shutdown. In this work, transient liquid water removal processes in the FF channels and GDLs are visualized and quantified by subsecond in situ X-ray tomographic microscopy (XTM), and correlated to high frequency resistance (HFR) measurements of the cell. Time-resolved desaturation profiles are analyzed for three commercially available GDLs with representative substrate dimensions. The influence of different substrates on the GDL desaturation behavior is investigated with a cluster connectivity analysis and saturation-dependent effective diffusivities are determined by numerical simulations. Characteristic drying phases are identified for the HFR curves and confirmed with XTM imaging results, providing fundamental understanding of the desaturation dynamics in the PEFCs and enabling the optimization of GDL substrates and gas purge protocols accordingly.
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3YA00189J
Abstract: Water distribution in the microporous layer (MPL) and the gas diffusion layer (GDL) substrate during PEFC operation at different conditions is quantitatively measured by X-ray tomographic microscopy (XTM) with time resolution down to a few seconds to probe the underlying water transport mechanism.
Publisher: American Chemical Society (ACS)
Date: 27-11-2013
DOI: 10.1021/JP4057169
Publisher: American Chemical Society (ACS)
Date: 25-05-2023
Publisher: American Chemical Society (ACS)
Date: 08-07-2021
Publisher: The Electrochemical Society
Date: 09-06-2011
DOI: 10.1149/1.3596556
Abstract: Water management is an important factor for optimizing polymer electrolyte fuel cells (PEFC) under high current density conditions as required for the automotive application. The characteristics of the local liquid saturation of the gas diffusion layer (GDL) is of particular interest. Here we report on the development of in-situ X-ray tomographic microscopy (XTM) with a pixel sizes in the order of 2 μm and sensitivity for carbon and liquid water for the quantitative analysis of liquid water in GDLs. In-situ XTM of PEFC is a major experimental challenge. A complete cell needs to be operated under realistic conditions in the constraint space of the small field of view on the beamline s le stage. Further phase segmentation of the images is required to successfully analyze the quantitative properties of the different phases. For this a workflow, applying differential images between dry and wet structures has been developed. Cells with Toray TGP-H-060 GDLs were analyzed in-situ. Droplets that appear on the GDL surface are connected to a significant water structure inside the GDL. Further the water cluster size distribution in the GDL shows that while small droplets ( pl) are numerous, most of the water is contained in few larger clusters.
Publisher: Elsevier BV
Date: 2014
Publisher: The Electrochemical Society
Date: 04-10-2011
DOI: 10.1149/1.3635570
Abstract: In X-ray tomography experiments, a significant decay of the performance of operating PEFC was observed when the entire active area is irradiated. Therefore, the dose dependent influence of synchrotron radiation at 13.5 keV on the mechanical and chemical properties of membranes, gas diffusion layers, electrodes and PTFE is investigated. The PEFC performance decays when exposed for more than about 100 s. On the same timescale, the strength of break of PTFE and membranes and the equivalent weight of the membrane decreases. IR-spectra of irradiated membranes show new features, increasing with exposure time and the wetting properties are influenced. The integrity of the catalyst layer on the electrodes, as well as on the CCM suffers to a large extent.
Publisher: SPIE
Date: 19-08-2010
DOI: 10.1117/12.860208
Publisher: The Electrochemical Society
Date: 04-10-2011
DOI: 10.1149/1.3635572
Abstract: Synchrotron radiation X-ray tomographic microscopy (SRXTM) allows the simultaneous in-situ visualization of the water and carbonaceous structures in the gas diffusion layer (GDL) of polymer electrolyte fuel cells (PEFC) on the pore scale. Recently, the TOMCAT beamline of the Swiss Light Source (SLS) was upgraded with a new CMOS camera, enabling ultra fast in-situ XTM investigations of PEFC with temporal resolution of about 8 s. This acquisition speed limits irradiation of the cell, preventing radiation damage and subsequent measurement bias. In this way, PEFC can be imaged several times before deterioration is arising. The stability of the 3D liquid water distribution in porous GDL structures was studied with a temporal resolution of 10 minutes and liquid water fraction data is presented.
Publisher: The Electrochemical Society
Date: 10-2010
DOI: 10.1149/1.3484631
Abstract: In-situ synchrotron-based tomographic microscopy (SRXTM) with a spatial resolution in the order of 1μm and sensitivity for carbon and liquid water, has the potential to provide fundamental information for the understanding of the wetting properties of gas diffusion layer (GDL) materials on the pore level. This is important for the understanding of the solid-water interactions in the porous structures since water transport in GDLs is considered a key transport mechanism polymer electrolyte fuel cells (PEFC). However SRXTM of PEFC is a major experimental challenge. To obtain quantitative results, a complete cell needs to be operated under realistic conditions in the constrained space of the small field of view on the beamline s le stage without disturbing the s le rotation.
Publisher: Global Science Press
Date: 03-2013
DOI: 10.4208/CICP.341011.310112S
Abstract: A 3D lattice Boltzmann (LB) model with twenty-seven discrete velocities is presented and used for the simulation of three-dimensional porous media flows. Its accuracy in combination with the half-way bounce back boundary condition is assessed. Characteristic properties of the gas diffusion layers that are used in polymer electrolyte fuel cells can be determined with this model. Simulation in s les that have been obtained via X-ray tomographic microscopy, allows to estimate the values of permeability and relative effective diffusivity. Furthermore, the computational LB results are compared with the results of other numerical tools, as well as with experimental values.
Publisher: The Electrochemical Society
Date: 2012
DOI: 10.1149/2.005209JES
Publisher: The Electrochemical Society
Date: 07-2021
Abstract: Gas diffusion layers (GDLs) are commonly known as one of the critical water management components in polymer electrolyte fuel cells with significant impact on the electrochemical cell performance. Increasing levels of liquid saturation in GDLs, especially during high-current-density operation, limit gas transport from the flow field channels to the catalyst layer surfaces and hence reduce cell performance. To provide GDL material selection and modification guidelines, a thorough understanding of the underlying structural factors of GDL materials and their influence on water management is required. In this work, operando X-ray tomographic microscopy (XTM) was employed to investigate the liquid saturation behavior for three commercial GDL materials during i-E curves and current jump characterization. Liquid volume fractions, saturation profiles and cluster distributions were analyzed to understand observed discrepancies in cell performance. Furthermore, saturation-dependent relative diffusivities were derived via direct numerical simulations, and the impact of GDL substrates on cell performance is thoroughly discussed with respect to structure and thermal properties.
No related grants have been discovered for Jens Eller.